diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 31eb1a1..14e89f4 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -56,6 +56,7 @@ jobs:
                     - "8.1"
                     - "8.2"
                     - "8.3"
+                    - "8.4"
 
                 dependencies:
                     - "lowest"
@@ -92,6 +93,7 @@ jobs:
                     - "8.1"
                     - "8.2"
                     - "8.3"
+                    - "8.4"
 
                 dependencies:
                     - "lowest"
@@ -127,6 +129,7 @@ jobs:
                     - "8.1"
                     - "8.2"
                     - "8.3"
+                    - "8.4"
 
                 dependencies:
                     - "lowest"
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..61d2c92
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,59 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## What this is
+
+A PHP SDK providing value objects and a client for Meta's (Facebook) [Conversions API](https://developers.facebook.com/docs/marketing-api/conversions-api). It is a library (`setono/meta-conversions-api-php-sdk`), not an application — there is no runnable entry point. Requires PHP >= 8.1.
+
+## Commands
+
+Composer scripts (defined in `composer.json`):
+
+- `composer phpunit` — run the test suite (PHPUnit 10)
+- `composer analyse` — PHPStan static analysis (`phpstan.dist.neon`: `level: max`, analysed against PHP 8.1)
+- `composer check-style` / `composer fix-style` — ECS coding-standard check / autofix
+- `vendor/bin/infection` — mutation testing (thresholds: minMsi 61.74, minCoveredMsi 76.77). Needs a coverage driver (pcov or Xdebug); CI uses pcov. With neither installed locally you'll get "No code coverage driver available".
+- `vendor/bin/composer-dependency-analyser` — verify declared composer deps match actual usage
+
+The dev tooling (PHPStan + extensions, ECS via `sylius-labs/coding-standard`, PHPUnit, Infection, Rector, composer-normalize, composer-dependency-analyser) is listed directly in `require-dev` rather than pulled in through the `setono/code-quality-pack` meta-package. The pack's current major requires PHP >= 8.2; inlining the tools keeps the whole toolchain runnable on PHP 8.1. When bumping a tool, pick the latest version that still supports PHP 8.1 (e.g. PHPUnit stays on `^10.5`, Infection on `^0.29`).
+
+Run a single test by file or filter:
+
+```bash
+vendor/bin/phpunit tests/Event/UserTest.php
+vendor/bin/phpunit --filter it_sends_event
+```
+
+Tests use the `@test` annotation with `snake_case` method names (no `test` prefix).
+
+CI (`.github/workflows/build.yaml`) runs coding standards, dependency analysis, PHPStan, and PHPUnit against PHP 8.1–8.4 on both `lowest` and `highest` dependency versions, so check lowest-version compatibility when touching dependencies. A separate workflow runs Roave's backwards-compatibility check on PRs — this is a public library, so avoid BC breaks to the public API.
+
+### LiveClientTest
+
+`tests/Client/LiveClientTest.php` hits the real Meta API. It self-skips unless the env vars in `phpunit.xml.dist` are set (`PIXEL_ID`, `ACCESS_TOKEN`, `TEST_EVENT_CODE`, `URL`, `EMAIL`). Copy `phpunit.xml.dist` to `phpunit.xml` and fill them in to run it.
+
+## Architecture
+
+The core abstraction is the serialization pipeline in `src/Event/Parameters.php`. Everything sent to Meta flows through it.
+
+**`Parameters` (abstract base)** — each subclass implements `getMapping(string $context): array`, returning Meta's snake_case field names mapped to the object's (camelCase) PHP property values. `getPayload()` runs that mapping through `normalize()`, which recursively:
+1. formats `DateTimeInterface` as `Ymd` and casts `Stringable` to string,
+2. normalizes fields listed in `getNormalizedFields()` via `FacebookAds\Object\ServerSide\Normalizer`,
+3. hashes fields listed in `getHashedFields()` via `FacebookAds\Object\ServerSide\Util::hash` (SHA-256 — this is how PII like email/phone is protected),
+4. recurses into nested `Parameters` objects (calling their `getPayload()`),
+5. strips empty values (`null`, `''`, `[]`) so they aren't sent.
+
+So to add a field: add the public property, map it in `getMapping()`, and register it in `getNormalizedFields()`/`getHashedFields()` if Meta requires it. The lists of which fields normalize/hash mirror the corresponding `FacebookAds\Object\ServerSide\*` classes (see the `@see` annotations) — keep them in sync with that SDK.
+
+**Two payload contexts** (`PAYLOAD_CONTEXT_SERVER` vs `PAYLOAD_CONTEXT_BROWSER`). The same objects serialize differently depending on whether they're sent server-side via the Conversions API or rendered into a client-side `fbq()` call. `User::getMapping()` strips server-only fields (IP, user agent, fbc, fbp) in browser context.
+
+**`Parameters` subclasses:** `Event` (the aggregate root — holds `User $userData`, `Custom $customData`, a list of `Pixel`, plus `metadata` for app-internal use that is never sent), `User` (customer matching data), `Custom` (event-specific data like value/currency/contents). `Event` auto-generates `eventId` (random, for [deduplication](https://developers.facebook.com/docs/marketing-api/conversions-api/parameters/server-event#event-id)) and `eventTime` in its constructor. `Event` is intentionally **not** `final` so consumers can subclass it into domain-specific events; the other data objects are `final`.
+
+**`Client` (`src/Client/Client.php`)** — `sendEvent()` serializes the event once, then POSTs it (form-encoded) to `graph.facebook.com/v{ApiConfig::APIVersion}/{pixelId}/events` once per associated pixel (each pixel carries its own access token). Non-200 responses throw `ClientException` built from `ErrorResponse`. HTTP is fully PSR-based: PSR-18 client and PSR-17 factories are auto-discovered via `php-http/discovery` but can be injected with `setHttpClient()` / `setRequestFactory()` / etc. The client is `LoggerAware` and defaults to `NullLogger`.
+
+**`FbqGenerator` (`src/Generator/FbqGenerator.php`)** — the client-side counterpart. Generates the `fbq('init', ...)` / `fbq('track', ...)` JavaScript snippets, using the browser-context payload and reusing the same `eventId` so server and browser events deduplicate. `Event::isCustom()` decides between `track` and `trackCustom`.
+
+**Value objects (`src/ValueObject/`)** — `Fbc`/`Fbp` (extending `Fb`) model the `_fbc`/`_fbp` cookie values with `fromString()` validation and `value()` serialization; assignable to `User::$fbc`/`$fbp` as either the typed object or a raw string.
+
+The `facebook/php-business-sdk` dependency is used only for `Normalizer`, `Util::hash`, and `ApiConfig::APIVersion` (the API version is pinned to whatever that package ships).
diff --git a/LICENSE b/LICENSE
index e4c0848..84b974a 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2025 Setono
+Copyright (c) 2026 Setono
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/README.md b/README.md
index ca6023e..88bb458 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# PHP library with basic objects and more for working with Facebook/Metas Conversions API
+# Meta (Facebook) Conversions API PHP SDK
 
 [![Latest Version][ico-version]][link-packagist]
 [![Software License][ico-license]](LICENSE)
@@ -6,34 +6,233 @@
 [![Code Coverage][ico-code-coverage]][link-code-coverage]
 [![Mutation testing][ico-infection]][link-infection]
 
+A small, typed PHP library for sending server-side events to Meta's (Facebook's)
+[Conversions API](https://developers.facebook.com/docs/marketing-api/conversions-api), and for generating the
+matching browser-side `fbq()` snippets.
+
+It gives you plain, well-typed objects (`Event`, `User`, `Custom`, …) and takes care of the fiddly parts for you:
+
+- **Automatic normalization & hashing** of customer information — you pass raw emails, phone numbers, names, etc. and
+  the SDK normalizes and SHA-256 hashes them the way Meta requires. Never hash this data yourself.
+- **Server + browser deduplication** — every event gets an `eventId` you can reuse on both sides so Meta counts it once.
+- **Bring your own HTTP client** — built on PSR-18/PSR-17 with auto-discovery, so it works with any compliant client.
+
+## Requirements
+
+- PHP 8.1+
+- A [PSR-18](https://www.php-fig.org/psr/psr-18/) HTTP client and [PSR-17](https://www.php-fig.org/psr/psr-17/) factories
+  (see [Installation](#installation))
+
 ## Installation
 
-The easiest way to install this library is by installing the library along with its HTTP client dependencies:
+The SDK talks to the API through a PSR-18 client and PSR-17 factories, which it discovers automatically. The simplest
+way is to install it together with an implementation:
 
 ```bash
 composer require setono/meta-conversions-api-php-sdk kriswallsmith/buzz nyholm/psr7
 ```
 
-If you want to use your own HTTP client, just do `composer require setono/meta-conversions-api-php-sdk` and then
-remember to set the HTTP client and factories when instantiating the `Setono\MetaConversionsApi\Client\Client`
+`symfony/http-client` works just as well if you prefer it:
 
-## Usage
+```bash
+composer require setono/meta-conversions-api-php-sdk symfony/http-client nyholm/psr7
+```
+
+If your project already ships a PSR-18 client and PSR-17 factories you only need the SDK itself
+(`composer require setono/meta-conversions-api-php-sdk`); see [Using your own HTTP client](#using-your-own-http-client).
+
+## Quick start
 
 ```php
+use Setono\MetaConversionsApi\Client\Client;
 use Setono\MetaConversionsApi\Event\Event;
 use Setono\MetaConversionsApi\Pixel\Pixel;
 
 $event = new Event(Event::EVENT_VIEW_CONTENT);
 $event->eventSourceUrl = 'https://example.com/products/blue-jeans';
-$event->userData->clientUserAgent = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.0.0 Safari/537.36';
-$event->userData->email[] = 'johndoe@example.com';
-$event->pixels[] = new Pixel('INSERT YOUR PIXEL ID', 'INSERT YOUR ACCESS TOKEN');
-// $event->testEventCode = 'test event code'; // uncomment this if you want to send a test event
+$event->userData->clientUserAgent = $_SERVER['HTTP_USER_AGENT'];
+$event->userData->clientIpAddress = $_SERVER['REMOTE_ADDR'];
+$event->userData->email[] = 'johndoe@example.com'; // hashed for you before sending
+
+// A pixel carries the id and the access token used to authenticate the request
+$event->pixels[] = new Pixel('YOUR_PIXEL_ID', 'YOUR_ACCESS_TOKEN');
 
 $client = new Client();
 $client->sendEvent($event);
 ```
 
+An `Event` is created with a random `eventId` and the current `eventTime` already set, and defaults to the `website`
+action source. Pass a different source as the second constructor argument if needed (e.g.
+`new Event(Event::EVENT_PURCHASE, Event::ACTION_SOURCE_PHYSICAL_STORE)`).
+
+## Sending a richer event
+
+`Event::$customData` holds the event-specific data (value, currency, contents, …) and `Event::$userData` holds the
+customer-matching data:
+
+```php
+use Setono\MetaConversionsApi\Client\Client;
+use Setono\MetaConversionsApi\Event\Content;
+use Setono\MetaConversionsApi\Event\Event;
+use Setono\MetaConversionsApi\Pixel\Pixel;
+
+$event = new Event(Event::EVENT_PURCHASE);
+$event->eventSourceUrl = 'https://example.com/checkout/complete';
+
+// Customer information — pass raw values, the SDK normalizes and hashes them
+$event->userData->email[] = 'johndoe@example.com';
+$event->userData->phoneNumber[] = '+1 (555) 123-4567';
+$event->userData->firstName[] = 'John';
+$event->userData->lastName[] = 'Doe';
+$event->userData->clientUserAgent = $_SERVER['HTTP_USER_AGENT'];
+$event->userData->clientIpAddress = $_SERVER['REMOTE_ADDR'];
+
+// Event data
+$event->customData->currency = 'USD';
+$event->customData->value = 142.52;
+$event->customData->contents[] = new Content('SKU-1', 1, 99.99);
+$event->customData->contents[] = new Content('SKU-2', 1, 42.53);
+
+// Anything not covered by a typed property can go into customProperties
+$event->customData->customProperties['membership_level'] = 'gold';
+
+$event->pixels[] = new Pixel('YOUR_PIXEL_ID', 'YOUR_ACCESS_TOKEN');
+
+(new Client())->sendEvent($event);
+```
+
+### Multiple pixels
+
+Add more than one `Pixel` and the event is sent to each of them (every pixel carries its own access token):
+
+```php
+$event->pixels[] = new Pixel('PIXEL_ID_1', 'ACCESS_TOKEN_1');
+$event->pixels[] = new Pixel('PIXEL_ID_2', 'ACCESS_TOKEN_2');
+```
+
+### Test events
+
+While integrating, set a test event code so the event shows up in the *Test events* tool in Events Manager instead of
+counting as real traffic:
+
+```php
+$event->testEventCode = 'TEST12345';
+```
+
+### Error handling
+
+`sendEvent()` throws a `ClientException` if Meta returns a non-2xx response. The message contains Meta's error message,
+code, trace id and the raw response (including the user-facing explanation when Meta provides one):
+
+```php
+use Setono\MetaConversionsApi\Exception\ClientException;
+
+try {
+    $client->sendEvent($event);
+} catch (ClientException $e) {
+    $logger->error('Could not send event to Meta', ['exception' => $e]);
+}
+```
+
+## Browser-side tracking with deduplication
+
+To get the best match quality Meta recommends sending events both server-side (this SDK) *and* from the browser, using
+the same `eventId` so they are deduplicated. `FbqGenerator` produces the matching JavaScript:
+
+```php
+use Setono\MetaConversionsApi\Event\Parameters;
+use Setono\MetaConversionsApi\Generator\FbqGenerator;
+
+$generator = new FbqGenerator();
+
+// In your <head>: initialise the pixel(s) and send a PageView
+echo $generator->generateInit(
+    $event->pixels,
+    $event->userData->getPayload(Parameters::PAYLOAD_CONTEXT_BROWSER),
+);
+
+// Where the conversion happens: fire the same event in the browser.
+// Because it reuses $event->eventId, Meta counts the server + browser event once.
+echo $generator->generateTrack($event);
+```
+
+Both methods wrap the output in a `<script>` tag by default; pass `false` as the last argument to get the raw
+JavaScript instead (e.g. to combine several calls into one tag).
+
+## Custom events
+
+Any event name that isn't one of the standard `Event::EVENT_*` constants is treated as a
+[custom event](https://developers.facebook.com/docs/meta-pixel/implementation/conversion-tracking#custom-events).
+`FbqGenerator` will emit `trackCustom` instead of `track` for these:
+
+```php
+$event = new Event('SubscribedToNewsletter');
+$event->isCustom(); // true
+```
+
+## `fbc` / `fbp` cookies
+
+The `_fbc` and `_fbp` cookies improve attribution. Assign them to the user data either as raw strings or as the typed
+value objects, which validate the format:
+
+```php
+use Setono\MetaConversionsApi\ValueObject\Fbc;
+use Setono\MetaConversionsApi\ValueObject\Fbp;
+
+$event->userData->fbc = Fbc::fromString($_COOKIE['_fbc']);
+$event->userData->fbp = Fbp::fromString($_COOKIE['_fbp']);
+```
+
+## Using your own HTTP client
+
+By default the client auto-discovers a PSR-18 client and PSR-17 factories. To inject your own (e.g. a preconfigured
+Guzzle client with timeouts and retries), use the setters:
+
+```php
+$client = new Client();
+$client->setHttpClient($myPsr18Client);
+$client->setRequestFactory($myPsr17RequestFactory);
+$client->setStreamFactory($myPsr17StreamFactory);
+```
+
+## Logging
+
+`Client` is `LoggerAware`. Pass any PSR-3 logger and the SDK will, for example, warn you when you try to send an event
+that has no pixels associated:
+
+```php
+$client->setLogger($logger);
+```
+
+## Extending events
+
+`Event` is intentionally **not** `final`, so you can build domain-specific events with sensible defaults:
+
+```php
+use Setono\MetaConversionsApi\Event\Event;
+
+final class PurchaseEvent extends Event
+{
+    public function __construct()
+    {
+        parent::__construct(self::EVENT_PURCHASE);
+    }
+}
+```
+
+## Development
+
+```bash
+composer phpunit       # run the test suite
+composer analyse       # static analysis (PHPStan)
+composer check-style   # coding standard check (ECS)
+composer fix-style     # fix coding standard violations
+```
+
+## License
+
+This library is released under the [MIT License](LICENSE).
+
 [ico-version]: https://poser.pugx.org/setono/meta-conversions-api-php-sdk/v/stable
 [ico-license]: https://poser.pugx.org/setono/meta-conversions-api-php-sdk/license
 [ico-github-actions]: https://github.com/Setono/meta-conversions-api-php-sdk/actions/workflows/build.yaml/badge.svg
diff --git a/composer.json b/composer.json
index c33a154..014c86a 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,7 @@
     "require": {
         "php": ">=8.1",
         "ext-json": "*",
-        "facebook/php-business-sdk": "^22.0",
+        "facebook/php-business-sdk": "^25.0",
         "php-http/discovery": "^1.20",
         "psr/http-client": "^1.0",
         "psr/http-client-implementation": "*",
@@ -22,12 +22,20 @@
         "webmozart/assert": "^1.11"
     },
     "require-dev": {
-        "infection/infection": "^0.26.21",
+        "ergebnis/composer-normalize": "^2.50",
+        "infection/infection": "^0.29",
+        "jangregor/phpstan-prophecy": "^2.3",
         "nyholm/psr7": "^1.8",
-        "phpunit/phpunit": "^9.6",
-        "psalm/plugin-phpunit": "^0.19",
-        "setono/code-quality-pack": "^2.9",
-        "shipmonk/composer-dependency-analyser": "^1.8.2",
+        "phpspec/prophecy-phpunit": "^2.5",
+        "phpstan/extension-installer": "^1.4",
+        "phpstan/phpstan": "^2.1",
+        "phpstan/phpstan-phpunit": "^2.0",
+        "phpstan/phpstan-strict-rules": "^2.0",
+        "phpstan/phpstan-webmozart-assert": "^2.0",
+        "phpunit/phpunit": "^10.5",
+        "rector/rector": "^2.4",
+        "shipmonk/composer-dependency-analyser": "^1.8",
+        "sylius-labs/coding-standard": "^4.5",
         "symfony/http-client": "^6.4 || ^7.0"
     },
     "prefer-stable": true,
@@ -46,12 +54,13 @@
             "dealerdirect/phpcodesniffer-composer-installer": false,
             "ergebnis/composer-normalize": true,
             "infection/extension-installer": true,
-            "php-http/discovery": false
+            "php-http/discovery": false,
+            "phpstan/extension-installer": true
         },
         "sort-packages": true
     },
     "scripts": {
-        "analyse": "psalm",
+        "analyse": "phpstan analyse",
         "check-style": "ecs check",
         "fix-style": "ecs check --fix",
         "phpunit": "phpunit"
diff --git a/phpstan.dist.neon b/phpstan.dist.neon
new file mode 100644
index 0000000..ca7eec6
--- /dev/null
+++ b/phpstan.dist.neon
@@ -0,0 +1,6 @@
+parameters:
+    level: max
+    treatPhpDocTypesAsCertain: false
+    paths:
+        - src
+        - tests
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 435518b..0bd36fe 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd" bootstrap="vendor/autoload.php"
-         colors="true" verbose="true">
-    <coverage includeUncoveredFiles="true" processUncoveredFiles="true">
-        <include>
-            <directory suffix=".php">src/</directory>
-        </include>
-    </coverage>
+         colors="true">
     <testsuites>
-        <testsuite name="Codex Editor PHP Test Suite">
+        <testsuite name="Meta Conversions API PHP SDK Test Suite">
             <directory>tests</directory>
         </testsuite>
     </testsuites>
+    <source>
+        <include>
+            <directory suffix=".php">src</directory>
+        </include>
+    </source>
     <php>
         <env name="PIXEL_ID" value=""/>
         <env name="TEST_EVENT_CODE" value=""/>
diff --git a/psalm.xml b/psalm.xml
deleted file mode 100644
index 50c840d..0000000
--- a/psalm.xml
+++ /dev/null
@@ -1,23 +0,0 @@
-<?xml version="1.0"?>
-<psalm
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xmlns="https://getpsalm.org/schema/config"
-    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
-    findUnusedVariablesAndParams="false"
-    findUnusedPsalmSuppress="false"
-    findUnusedCode="false"
-    findUnusedBaselineEntry="false"
-    errorLevel="1"
-    phpVersion="8.1"
->
-    <projectFiles>
-        <directory name="src"/>
-        <directory name="tests"/>
-        <ignoreFiles>
-            <directory name="vendor"/>
-        </ignoreFiles>
-    </projectFiles>
-    <plugins>
-        <pluginClass class="Psalm\PhpUnitPlugin\Plugin"/>
-    </plugins>
-</psalm>
diff --git a/src/Client/Client.php b/src/Client/Client.php
index 9675716..c296969 100644
--- a/src/Client/Client.php
+++ b/src/Client/Client.php
@@ -23,8 +23,6 @@ final class Client implements ClientInterface, LoggerAwareInterface
 
     private ?RequestFactoryInterface $requestFactory = null;
 
-    private ?ResponseFactoryInterface $responseFactory = null;
-
     private ?StreamFactoryInterface $streamFactory = null;
 
     private LoggerInterface $logger;
@@ -101,18 +99,11 @@ public function setRequestFactory(RequestFactoryInterface $requestFactory): void
         $this->requestFactory = $requestFactory;
     }
 
-    private function getResponseFactory(): ResponseFactoryInterface
-    {
-        if (null === $this->responseFactory) {
-            $this->responseFactory = Psr17FactoryDiscovery::findResponseFactory();
-        }
-
-        return $this->responseFactory;
-    }
-
+    /**
+     * @deprecated the client does not create responses, so the response factory is not used; this method is kept for backwards compatibility only
+     */
     public function setResponseFactory(ResponseFactoryInterface $responseFactory): void
     {
-        $this->responseFactory = $responseFactory;
     }
 
     private function getStreamFactory(): StreamFactoryInterface
diff --git a/src/Client/ErrorResponse.php b/src/Client/ErrorResponse.php
index 5477d67..186f424 100644
--- a/src/Client/ErrorResponse.php
+++ b/src/Client/ErrorResponse.php
@@ -8,9 +8,18 @@
 use Webmozart\Assert\Assert;
 
 /**
- * todo also handle a JSON response like this:
+ * Represents the error envelope Meta/Facebook returns when a request fails.
  *
- * {"error":{"message":"Invalid parameter","type":"OAuthException","code":100,"error_subcode":2804050,"is_transient":false,"error_user_title":"Du har ikke tilf\u00f8jet tilstr\u00e6kkelige data om kundeoplysningsparametre for denne h\u00e6ndelse","error_user_msg":"Denne h\u00e6ndelse har ingen kundeoplysningsparametre, eller den har en kombination af kundeoplysningsparametre, der er s\u00e5 bred, at det er usandsynligt, at det vil v\u00e6re effektivt til matchning. Du kan l\u00f8se dette ved at g\u00e5 til de anbefalede fremgangsm\u00e5der for parametre p\u00e5 developers.facebook.com\/docs\/marketing-api\/conversions-api\/best-practices\/#req-rec-params","fbtrace_id":"Asu2mk752HZ0oT07IksFAwN"}}
+ * The minimal shape is:
+ *
+ *     {"error":{"message":"..","type":"..","code":100,"fbtrace_id":".."}}
+ *
+ * but Meta may also send the optional error_subcode, is_transient and the user facing
+ * error_user_title / error_user_msg fields, e.g.:
+ *
+ *     {"error":{"message":"Invalid parameter","type":"OAuthException","code":100,"error_subcode":2804050,"is_transient":false,"error_user_title":"..","error_user_msg":"..","fbtrace_id":".."}}
+ *
+ * Those optional fields are captured when present.
  *
  * @internal
  */
@@ -29,6 +38,14 @@ final class ErrorResponse
 
     public string $traceId;
 
+    public ?int $subcode = null;
+
+    public ?bool $transient = null;
+
+    public ?string $userTitle = null;
+
+    public ?string $userMessage = null;
+
     private function __construct(string $json, string $message, string $type, int $code, string $traceId)
     {
         $this->json = $json;
@@ -51,21 +68,43 @@ public static function fromJson(string $json): self
 
         try {
             Assert::isArray($data);
+            Assert::keyExists($data, 'error');
+
+            $error = $data['error'];
+            Assert::isArray($error);
 
-            if (!isset($data['error']['message'], $data['error']['type'], $data['error']['code'], $data['error']['fbtrace_id'])) {
+            if (!isset($error['message'], $error['type'], $error['code'], $error['fbtrace_id'])) {
                 throw ClientException::invalidResponseFormat($json);
             }
 
-            ['message' => $message, 'type' => $type, 'code' => $code, 'fbtrace_id' => $traceId] = $data['error'];
+            ['message' => $message, 'type' => $type, 'code' => $code, 'fbtrace_id' => $traceId] = $error;
 
             Assert::string($message);
             Assert::string($type);
             Assert::integer($code);
             Assert::string($traceId);
+
+            $subcode = $error['error_subcode'] ?? null;
+            Assert::nullOrInteger($subcode);
+
+            $transient = $error['is_transient'] ?? null;
+            Assert::nullOrBoolean($transient);
+
+            $userTitle = $error['error_user_title'] ?? null;
+            Assert::nullOrString($userTitle);
+
+            $userMessage = $error['error_user_msg'] ?? null;
+            Assert::nullOrString($userMessage);
         } catch (\InvalidArgumentException $e) {
             throw ClientException::invalidResponseFormat($json);
         }
 
-        return new self($json, $message, $type, $code, $traceId);
+        $self = new self($json, $message, $type, $code, $traceId);
+        $self->subcode = $subcode;
+        $self->transient = $transient;
+        $self->userTitle = $userTitle;
+        $self->userMessage = $userMessage;
+
+        return $self;
     }
 }
diff --git a/src/Event/Content.php b/src/Event/Content.php
index 328280b..e1e6407 100644
--- a/src/Event/Content.php
+++ b/src/Event/Content.php
@@ -15,10 +15,10 @@ final class Content extends Parameters
     public ?string $deliveryCategory;
 
     public function __construct(
-        string $id = null,
-        int $quantity = null,
-        float $itemPrice = null,
-        string $deliveryCategory = null,
+        ?string $id = null,
+        ?int $quantity = null,
+        ?float $itemPrice = null,
+        ?string $deliveryCategory = null,
     ) {
         $this->id = $id;
         $this->quantity = $quantity;
diff --git a/src/Event/Event.php b/src/Event/Event.php
index 3224d82..ff1797a 100644
--- a/src/Event/Event.php
+++ b/src/Event/Event.php
@@ -92,6 +92,7 @@ class Event extends Parameters
 
     public ?string $actionSource = null;
 
+    /** @var list<string> */
     public array $dataProcessingOptions = [];
 
     public ?int $dataProcessingOptionsCountry = null;
diff --git a/src/Event/Parameters.php b/src/Event/Parameters.php
index 402bd83..7bf1354 100644
--- a/src/Event/Parameters.php
+++ b/src/Event/Parameters.php
@@ -17,13 +17,20 @@ abstract class Parameters
     /**
      * This method returns an array representation of the object ready
      * to be sent to Meta/Facebook, i.e. it's both normalized and hashed
+     *
+     * @return array<string, mixed>
      */
     public function getPayload(string $context = self::PAYLOAD_CONTEXT_SERVER): array
     {
-        $payload = self::normalize($this->getMapping($context));
-        Assert::isArray($payload);
+        // The mapping keys are field names (strings), so iterating here lets the return type stay the precise
+        // array<string, mixed> that consumers like FbqGenerator::generateInit() rely on. The recursive normalize()
+        // below works on values of unknown key type, hence it can only yield array<array-key, mixed>.
+        $payload = [];
+        foreach ($this->getMapping($context) as $field => $value) {
+            $payload[$field] = $value instanceof self ? $value->getPayload() : self::normalize($value, $field);
+        }
 
-        return $payload;
+        return self::filterEmptyValues($payload);
     }
 
     /**
@@ -53,9 +60,9 @@ protected static function getHashedFields(): array
     /**
      * @param mixed $data
      *
-     * @return array|string|float|int|bool|null
+     * @return array<array-key, mixed>|string|float|int|bool|null
      */
-    private static function normalize($data, string $field = null)
+    private static function normalize($data, ?string $field = null)
     {
         if (null === $data) {
             return null;
@@ -98,7 +105,20 @@ private static function normalize($data, string $field = null)
         }
         unset($datum);
 
-        // this will filter values we don't want to send to Meta/Facebook, i.e. nulls, empty strings, and empty arrays
+        return self::filterEmptyValues($data);
+    }
+
+    /**
+     * Filters out the values we don't want to send to Meta/Facebook, i.e. nulls, empty strings, and empty arrays
+     *
+     * @template TKey of array-key
+     *
+     * @param array<TKey, mixed> $data
+     *
+     * @return array<TKey, mixed>
+     */
+    private static function filterEmptyValues(array $data): array
+    {
         return array_filter($data, static function ($value): bool {
             return !(null === $value || '' === $value || [] === $value);
         });
diff --git a/src/Exception/ClientException.php b/src/Exception/ClientException.php
index 9911b03..cced96e 100644
--- a/src/Exception/ClientException.php
+++ b/src/Exception/ClientException.php
@@ -32,14 +32,25 @@ public static function invalidResponseFormat(string $json): self
     public static function fromErrorResponse(ErrorResponse $errorResponse): self
     {
         $message = sprintf(
-            "An error occurred sending an event to Meta/Facebook: %s (code: %d, type: %s, trace id: %s)\n\nRaw JSON response:\n\n%s",
+            'An error occurred sending an event to Meta/Facebook: %s (code: %d',
             $errorResponse->message,
             $errorResponse->code,
-            $errorResponse->type,
-            $errorResponse->traceId,
-            $errorResponse->json,
         );
 
+        if (null !== $errorResponse->subcode) {
+            $message .= sprintf(', subcode: %d', $errorResponse->subcode);
+        }
+
+        $message .= sprintf(', type: %s, trace id: %s)', $errorResponse->type, $errorResponse->traceId);
+
+        // The user_* fields, when present, hold a human readable explanation aimed at the end user
+        $userMessage = trim(sprintf('%s %s', $errorResponse->userTitle ?? '', $errorResponse->userMessage ?? ''));
+        if ('' !== $userMessage) {
+            $message .= sprintf("\n\n%s", $userMessage);
+        }
+
+        $message .= sprintf("\n\nRaw JSON response:\n\n%s", $errorResponse->json);
+
         return new self($message);
     }
 }
diff --git a/src/Generator/FbqGenerator.php b/src/Generator/FbqGenerator.php
index 89b8b6b..d75312a 100644
--- a/src/Generator/FbqGenerator.php
+++ b/src/Generator/FbqGenerator.php
@@ -9,6 +9,7 @@
 use Psr\Log\NullLogger;
 use Setono\MetaConversionsApi\Event\Event;
 use Setono\MetaConversionsApi\Event\Parameters;
+use Setono\MetaConversionsApi\Pixel\Pixel;
 
 final class FbqGenerator implements FbqGeneratorInterface, LoggerAwareInterface
 {
@@ -19,6 +20,10 @@ public function __construct()
         $this->logger = new NullLogger();
     }
 
+    /**
+     * @param list<Pixel> $pixels
+     * @param array<string, mixed> $userData
+     */
     public function generateInit(
         array $pixels,
         array $userData = [],
diff --git a/src/Generator/FbqGeneratorInterface.php b/src/Generator/FbqGeneratorInterface.php
index 1012873..3b71d3a 100644
--- a/src/Generator/FbqGeneratorInterface.php
+++ b/src/Generator/FbqGeneratorInterface.php
@@ -13,6 +13,7 @@ interface FbqGeneratorInterface
      * Will generate the fbq() init call based on the given pixels. By default, this also includes the page view event
      *
      * @param list<Pixel> $pixels
+     * @param array<string, mixed> $userData
      */
     public function generateInit(
         array $pixels,
diff --git a/src/Pixel/Pixel.php b/src/Pixel/Pixel.php
index 99eb1a2..d967709 100644
--- a/src/Pixel/Pixel.php
+++ b/src/Pixel/Pixel.php
@@ -18,7 +18,7 @@ final class Pixel
      */
     public ?string $accessToken;
 
-    public function __construct(string $id, string $accessToken = null)
+    public function __construct(string $id, ?string $accessToken = null)
     {
         $this->id = $id;
         $this->accessToken = '' === $accessToken ? null : $accessToken;
diff --git a/src/ValueObject/Fb.php b/src/ValueObject/Fb.php
index ce94dce..060bcea 100644
--- a/src/ValueObject/Fb.php
+++ b/src/ValueObject/Fb.php
@@ -71,7 +71,6 @@ public function withCreationTime($creationTime): self
             $creationTime = (int) $creationTime->format('Uv');
         }
 
-        /** @psalm-suppress RedundantConditionGivenDocblockType */
         Assert::integer($creationTime);
         Assert::greaterThanEq($creationTime, 1_075_590_000_000); // Facebooks founding date xD
         Assert::lessThanEq($creationTime, (time() + 1) * 1000);
diff --git a/tests/Client/ClientTest.php b/tests/Client/ClientTest.php
index dc7a4e1..fe5b993 100644
--- a/tests/Client/ClientTest.php
+++ b/tests/Client/ClientTest.php
@@ -12,6 +12,7 @@
 use Psr\Http\Message\ResponseInterface;
 use Psr\Log\AbstractLogger;
 use Setono\MetaConversionsApi\Event\Event;
+use Setono\MetaConversionsApi\Exception\ClientException;
 use Setono\MetaConversionsApi\Pixel\Pixel;
 
 /**
@@ -39,10 +40,58 @@ public function it_sends_event(): void
 
         $request = $httpClient->requests[0];
         self::assertSame('POST', $request->getMethod());
-        self::assertSame('https://graph.facebook.com/v22.0/pixel_id/events', (string) $request->getUri());
+        self::assertSame('https://graph.facebook.com/v25.0/pixel_id/events', (string) $request->getUri());
         self::assertSame('data=%5B%7B%22event_name%22%3A%22Purchase%22%2C%22event_time%22%3A1658743659123%2C%22event_id%22%3A%22event_id%22%2C%22action_source%22%3A%22website%22%7D%5D', (string) $request->getBody());
     }
 
+    /**
+     * @test
+     */
+    public function it_includes_access_token_and_test_event_code_in_the_request(): void
+    {
+        $httpClient = new TestHttpClient();
+
+        $client = new Client();
+        $client->setHttpClient($httpClient);
+
+        $event = new Event(Event::EVENT_PURCHASE);
+        $event->pixels[] = new Pixel('pixel_id', 'access_token');
+        $event->testEventCode = 'TEST123';
+        $client->sendEvent($event);
+
+        self::assertCount(1, $httpClient->requests);
+
+        $body = (string) $httpClient->requests[0]->getBody();
+        self::assertStringContainsString('access_token=access_token', $body);
+        self::assertStringContainsString('test_event_code=TEST123', $body);
+    }
+
+    /**
+     * @test
+     */
+    public function it_throws_an_exception_when_the_response_is_not_successful(): void
+    {
+        $responseFactory = new Psr17Factory();
+
+        $httpClient = new TestHttpClient();
+        $httpClient->response = $responseFactory
+            ->createResponse(400)
+            ->withBody($responseFactory->createStream(
+                '{"error":{"message":"Invalid parameter","type":"OAuthException","code":100,"fbtrace_id":"trace123"}}',
+            ));
+
+        $client = new Client();
+        $client->setHttpClient($httpClient);
+
+        $event = new Event(Event::EVENT_PURCHASE);
+        $event->pixels[] = new Pixel('pixel_id', 'access_token');
+
+        $this->expectException(ClientException::class);
+        $this->expectExceptionMessage('Invalid parameter');
+
+        $client->sendEvent($event);
+    }
+
     /**
      * @test
      */
@@ -69,6 +118,8 @@ final class TestHttpClient implements HttpClientInterface
     /** @var list<RequestInterface> */
     public array $requests = [];
 
+    public ?ResponseInterface $response = null;
+
     public function __construct()
     {
         $this->responseFactory = new Psr17Factory();
@@ -78,7 +129,7 @@ public function sendRequest(RequestInterface $request): ResponseInterface
     {
         $this->requests[] = $request;
 
-        return $this->responseFactory->createResponse();
+        return $this->response ?? $this->responseFactory->createResponse();
     }
 }
 
@@ -90,6 +141,7 @@ final class TestLogger extends AbstractLogger
     /**
      * @param mixed $level
      * @param string|\Stringable $message
+     * @param array<array-key, mixed> $context
      */
     public function log($level, $message, array $context = []): void
     {
diff --git a/tests/Client/ErrorResponseTest.php b/tests/Client/ErrorResponseTest.php
new file mode 100644
index 0000000..12463c2
--- /dev/null
+++ b/tests/Client/ErrorResponseTest.php
@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Setono\MetaConversionsApi\Client;
+
+use PHPUnit\Framework\TestCase;
+use Setono\MetaConversionsApi\Exception\ClientException;
+
+/**
+ * @covers \Setono\MetaConversionsApi\Client\ErrorResponse
+ */
+final class ErrorResponseTest extends TestCase
+{
+    /**
+     * @test
+     */
+    public function it_parses_a_valid_error_response(): void
+    {
+        $json = '{"error":{"message":"Invalid parameter","type":"OAuthException","code":100,"fbtrace_id":"trace123"}}';
+
+        $errorResponse = ErrorResponse::fromJson($json);
+
+        self::assertSame($json, $errorResponse->json);
+        self::assertSame('Invalid parameter', $errorResponse->message);
+        self::assertSame('OAuthException', $errorResponse->type);
+        self::assertSame(100, $errorResponse->code);
+        self::assertSame('trace123', $errorResponse->traceId);
+
+        // the optional fields are null when not present
+        self::assertNull($errorResponse->subcode);
+        self::assertNull($errorResponse->transient);
+        self::assertNull($errorResponse->userTitle);
+        self::assertNull($errorResponse->userMessage);
+    }
+
+    /**
+     * @test
+     */
+    public function it_captures_the_optional_fields_when_present(): void
+    {
+        $json = '{"error":{"message":"Invalid parameter","type":"OAuthException","code":100,"error_subcode":2804050,"is_transient":false,"error_user_title":"Customer information parameters","error_user_msg":"This event has insufficient customer information.","fbtrace_id":"trace123"}}';
+
+        $errorResponse = ErrorResponse::fromJson($json);
+
+        self::assertSame('Invalid parameter', $errorResponse->message);
+        self::assertSame(100, $errorResponse->code);
+        self::assertSame(2804050, $errorResponse->subcode);
+        self::assertFalse($errorResponse->transient);
+        self::assertSame('Customer information parameters', $errorResponse->userTitle);
+        self::assertSame('This event has insufficient customer information.', $errorResponse->userMessage);
+        self::assertSame('trace123', $errorResponse->traceId);
+    }
+
+    /**
+     * @test
+     */
+    public function it_throws_when_the_response_is_not_valid_json(): void
+    {
+        $this->expectException(ClientException::class);
+
+        ErrorResponse::fromJson('this is not json');
+    }
+
+    /**
+     * @test
+     */
+    public function it_throws_when_the_response_is_not_an_array(): void
+    {
+        $this->expectException(ClientException::class);
+
+        ErrorResponse::fromJson('100');
+    }
+
+    /**
+     * @test
+     */
+    public function it_throws_when_the_error_key_is_missing(): void
+    {
+        $this->expectException(ClientException::class);
+
+        ErrorResponse::fromJson('{"foo":"bar"}');
+    }
+
+    /**
+     * @test
+     */
+    public function it_throws_when_a_field_has_the_wrong_type(): void
+    {
+        $this->expectException(ClientException::class);
+
+        // the code field must be an int
+        ErrorResponse::fromJson('{"error":{"message":"m","type":"t","code":"not-an-int","fbtrace_id":"x"}}');
+    }
+}
diff --git a/tests/Client/LiveClientTest.php b/tests/Client/LiveClientTest.php
index 5025c2f..76661cd 100644
--- a/tests/Client/LiveClientTest.php
+++ b/tests/Client/LiveClientTest.php
@@ -23,9 +23,12 @@ public function it_sends_event(): void
         try {
             $testValues = $this->getTestValues();
         } catch (\InvalidArgumentException $e) {
-            $this->markTestSkipped($e->getMessage());
+            self::markTestSkipped($e->getMessage());
         }
 
+        // the test passes as long as sending the event does not throw
+        $this->expectNotToPerformAssertions();
+
         $client = new Client();
 
         $event = new Event(Event::EVENT_VIEW_CONTENT);
@@ -36,35 +39,30 @@ public function it_sends_event(): void
         $event->testEventCode = $testValues['testEventCode'];
 
         $client->sendEvent($event);
-
-        self::assertTrue(true);
     }
 
     /**
      * @return array{pixelId: non-empty-string, testEventCode: non-empty-string, accessToken: non-empty-string, url: non-empty-string, email: non-empty-string}
-     *
-     * @psalm-suppress InvalidReturnType,MoreSpecificReturnType
      */
     private function getTestValues(): array
     {
-        $envVars = [
-            'pixelId' => 'PIXEL_ID',
-            'testEventCode' => 'TEST_EVENT_CODE',
-            'accessToken' => 'ACCESS_TOKEN',
-            'url' => 'URL',
-            'email' => 'EMAIL',
+        return [
+            'pixelId' => self::env('PIXEL_ID'),
+            'testEventCode' => self::env('TEST_EVENT_CODE'),
+            'accessToken' => self::env('ACCESS_TOKEN'),
+            'url' => self::env('URL'),
+            'email' => self::env('EMAIL'),
         ];
+    }
 
-        $values = [];
-
-        foreach ($envVars as $variable => $envVar) {
-            $value = getenv($envVar);
-            Assert::stringNotEmpty($value, sprintf('%s environment value is not set', $envVar));
-
-            $values[$variable] = $value;
-        }
+    /**
+     * @return non-empty-string
+     */
+    private static function env(string $name): string
+    {
+        $value = getenv($name);
+        Assert::stringNotEmpty($value, sprintf('%s environment value is not set', $name));
 
-        /** @psalm-suppress InvalidReturnStatement,LessSpecificReturnStatement */
-        return $values;
+        return $value;
     }
 }
diff --git a/tests/Event/ContentTest.php b/tests/Event/ContentTest.php
new file mode 100644
index 0000000..db706e0
--- /dev/null
+++ b/tests/Event/ContentTest.php
@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Setono\MetaConversionsApi\Event;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @covers \Setono\MetaConversionsApi\Event\Content
+ */
+final class ContentTest extends TestCase
+{
+    /**
+     * @test
+     */
+    public function it_generates_payload(): void
+    {
+        $content = new Content('product_id', 2, 99.95, 'home_delivery');
+
+        self::assertSame([
+            'id' => 'product_id',
+            'quantity' => 2,
+            'item_price' => 99.95,
+            'delivery_category' => 'home_delivery',
+        ], $content->getPayload());
+    }
+
+    /**
+     * @test
+     */
+    public function it_filters_empty_values_from_the_payload(): void
+    {
+        $content = new Content('product_id');
+
+        self::assertSame(['id' => 'product_id'], $content->getPayload());
+    }
+}
diff --git a/tests/Event/EventTest.php b/tests/Event/EventTest.php
index b0cc7cb..a267814 100644
--- a/tests/Event/EventTest.php
+++ b/tests/Event/EventTest.php
@@ -6,9 +6,82 @@
 
 use PHPUnit\Framework\TestCase;
 use Setono\MetaConversionsApi\Pixel\Pixel;
+use Setono\MetaConversionsApi\ValueObject\Fbc;
+use Setono\MetaConversionsApi\ValueObject\Fbp;
 
 final class EventTest extends TestCase
 {
+    /**
+     * Characterization test that pins the exact output of the whole serialization pipeline
+     * (nested Parameters objects, lists, scalars, normalization, hashing, value objects,
+     * custom properties and empty-value filtering) so any change to getPayload() is caught.
+     *
+     * @test
+     */
+    public function it_generates_the_full_payload(): void
+    {
+        $event = new Event(Event::EVENT_PURCHASE);
+        $event->eventTime = 1658743659;
+        $event->eventId = 'event_id';
+        $event->eventSourceUrl = 'https://example.com/checkout';
+        $event->optOut = false;
+        $event->dataProcessingOptions = ['LDU'];
+        $event->dataProcessingOptionsCountry = 1;
+        $event->dataProcessingOptionsState = 1000;
+
+        $event->userData->email[] = 'JohnDoe@Example.com';
+        $event->userData->phoneNumber[] = '+1 (555) 123-4567';
+        $event->userData->firstName[] = 'John';
+        $event->userData->lastName[] = 'Doe';
+        $event->userData->city[] = 'Copenhagen';
+        $event->userData->country[] = 'DK';
+        $event->userData->externalId[] = 'ext-123';
+        $event->userData->clientIpAddress = '192.168.0.1';
+        $event->userData->clientUserAgent = 'Chrome';
+        $event->userData->fbc = Fbc::fromString('fb.1.1657051589577.ClickId');
+        $event->userData->fbp = Fbp::fromString('fb.1.1656874832584.1088522659');
+
+        $event->customData->value = 110.5;
+        $event->customData->currency = 'DKK';
+        $event->customData->contentIds = ['PROD_1'];
+        $event->customData->contents[] = new Content('PROD_1', 2, 55.25, 'home_delivery');
+        $event->customData->customProperties['my_custom'] = 'x';
+
+        self::assertEquals([
+            'event_name' => 'Purchase',
+            'event_time' => 1658743659,
+            'user_data' => [
+                'em' => ['55e79200c1635b37ad31a378c39feb12f120f116625093a19bc32fff15041149'],
+                'ph' => ['d6736136ea896c1bfdc553e0e86e702c70d060d805696ca3e4e9e0961353860a'],
+                'fn' => ['96d9632f363564cc3032521409cf22a852f2032eec099ed5967c0d000cec607a'],
+                'ln' => ['799ef92a11af918e3fb741df42934f3b568ed2d93ac1df74f1b8d41a27932a6f'],
+                'ct' => ['842de7b239f0d6ab17dc08d3fcfe68c090a9af0eb5285cfbc5433b3304c5ebee'],
+                'country' => ['867b4bf4357a7c0e415ffd537f61ea8785dd47113104000b534a130c98a42ce8'],
+                'external_id' => ['ext-123'],
+                'client_ip_address' => '192.168.0.1',
+                'client_user_agent' => 'Chrome',
+                'fbc' => 'fb.1.1657051589577.ClickId',
+                'fbp' => 'fb.1.1656874832584.1088522659',
+            ],
+            'custom_data' => [
+                'my_custom' => 'x',
+                'content_ids' => ['PROD_1'],
+                'contents' => [
+                    ['id' => 'PROD_1', 'quantity' => 2, 'item_price' => 55.25, 'delivery_category' => 'home_delivery'],
+                ],
+                'currency' => 'dkk',
+                'value' => 110.5,
+            ],
+            'event_source_url' => 'https://example.com/checkout',
+            'opt_out' => false,
+            'event_id' => 'event_id',
+            'action_source' => 'website',
+            'data_processing_options' => ['LDU'],
+            'data_processing_options_country' => 1,
+            'data_processing_options_state' => 1000,
+        ], $event->getPayload());
+    }
+
     /**
      * @test
      */
@@ -41,14 +114,13 @@ public function it_filters(): void
         $event->eventTime = 123;
         $event->eventId = 'event_id';
         $event->userData->email[] = 'johndoe@example.com';
-        $event->userData->email[] = '';
-        /** @psalm-suppress InvalidPropertyAssignmentValue */
-        $event->userData->email[] = null;
-        /** @psalm-suppress InvalidPropertyAssignmentValue */
-        $event->userData->dateOfBirth[] = \DateTimeImmutable::createFromFormat('Y-m-d', '1986-07-11');
+        $event->userData->email[] = ''; // filtered out because it is empty
+
+        $dateOfBirth = \DateTimeImmutable::createFromFormat('Y-m-d', '1986-07-11');
+        self::assertNotFalse($dateOfBirth);
+        $event->userData->dateOfBirth[] = $dateOfBirth;
+
         $event->customData->contents[] = new Content('content_id', 1);
-        /** @psalm-suppress InvalidPropertyAssignmentValue */
-        $event->customData->contents[] = null;
 
         self::assertEquals([
             'event_id' => 'event_id',
@@ -71,6 +143,15 @@ public function it_filters(): void
         ], $event->getPayload());
     }
 
+    /**
+     * @test
+     */
+    public function it_knows_if_it_is_a_custom_event(): void
+    {
+        self::assertFalse((new Event(Event::EVENT_PURCHASE))->isCustom());
+        self::assertTrue((new Event('SomeNonStandardEvent'))->isCustom());
+    }
+
     /**
      * @test
      */
diff --git a/tests/Generator/FbqGeneratorTest.php b/tests/Generator/FbqGeneratorTest.php
index be3b476..7fcce24 100644
--- a/tests/Generator/FbqGeneratorTest.php
+++ b/tests/Generator/FbqGeneratorTest.php
@@ -21,8 +21,10 @@ public function it_generates_init(): void
         $event->pixels = [new Pixel('111'), new Pixel('222')];
         $event->userData->clientIpAddress = '192.168.0.1';
         $event->userData->clientUserAgent = 'Chrome';
-        /** @psalm-suppress InvalidPropertyAssignmentValue */
-        $event->userData->dateOfBirth[] = \DateTimeImmutable::createFromFormat('Y-m-d', '1986-07-11');
+
+        $dateOfBirth = \DateTimeImmutable::createFromFormat('Y-m-d', '1986-07-11');
+        self::assertNotFalse($dateOfBirth);
+        $event->userData->dateOfBirth[] = $dateOfBirth;
 
         $generator = new FbqGenerator();
         self::assertSame(<<<EXPECTED
@@ -36,6 +38,32 @@ public function it_generates_init(): void
             , $generator->generateInit($event->pixels, $event->userData->getPayload(Parameters::PAYLOAD_CONTEXT_BROWSER)));
     }
 
+    /**
+     * @test
+     */
+    public function it_generates_init_without_user_data(): void
+    {
+        $generator = new FbqGenerator();
+
+        self::assertSame(
+            "fbq('init', '111');fbq('init', '222');fbq('track', 'PageView');",
+            $generator->generateInit([new Pixel('111'), new Pixel('222')], [], true, false),
+        );
+    }
+
+    /**
+     * @test
+     */
+    public function it_generates_init_without_the_page_view(): void
+    {
+        $generator = new FbqGenerator();
+
+        self::assertSame(
+            "fbq('init', '111');",
+            $generator->generateInit([new Pixel('111')], [], false, false),
+        );
+    }
+
     /**
      * @test
      */
@@ -58,4 +86,20 @@ public function it_generates_track(): void
 EXPECTED
             , $generator->generateTrack($event));
     }
+
+    /**
+     * @test
+     */
+    public function it_generates_track_for_a_custom_event(): void
+    {
+        $event = new Event('MyCustomEvent');
+        $event->eventId = 'event_id';
+        $event->customData->value = 10.5;
+
+        $generator = new FbqGenerator();
+        self::assertSame(
+            "fbq('trackCustom', 'MyCustomEvent', {\"value\":10.5}, {eventID: 'event_id'});",
+            $generator->generateTrack($event, false),
+        );
+    }
 }
diff --git a/tests/ValueObject/FbcTest.php b/tests/ValueObject/FbcTest.php
index af0f9ad..ce7e1ab 100644
--- a/tests/ValueObject/FbcTest.php
+++ b/tests/ValueObject/FbcTest.php
@@ -50,6 +50,19 @@ public function it_has_immutable_setters(): void
         self::assertSame('NewClickId', $newFbc->getClickId());
     }
 
+    /**
+     * @test
+     */
+    public function it_has_immutable_creation_time_setter(): void
+    {
+        $fbc = Fbc::fromString('fb.1.1657051589577.ClickId');
+        $newFbc = $fbc->withCreationTime(1656874832584);
+
+        self::assertNotSame($fbc, $newFbc);
+        self::assertSame(1657051589577, $fbc->getCreationTime());
+        self::assertSame(1656874832584, $newFbc->getCreationTime());
+    }
+
     /**
      * @test
      *
@@ -64,7 +77,7 @@ public function it_handles_wrong_input(string $input): void
     /**
      * @return \Generator<array-key, array{string}>
      */
-    public function wrongInputs(): \Generator
+    public static function wrongInputs(): \Generator
     {
         yield ['wrong input'];
         yield ['afb.1.1657051589577.IwAR0rmfgHgxjdKoEopat9y2SPzyjGgfHm9AhdqygToWvarP59nPq15T07MiA'];
diff --git a/tests/ValueObject/FbpTest.php b/tests/ValueObject/FbpTest.php
index 32859be..2b0d0d5 100644
--- a/tests/ValueObject/FbpTest.php
+++ b/tests/ValueObject/FbpTest.php
@@ -57,7 +57,7 @@ public function it_handles_wrong_input(string $input): void
     /**
      * @return \Generator<array-key, array{string}>
      */
-    public function wrongInputs(): \Generator
+    public static function wrongInputs(): \Generator
     {
         yield ['wrong input'];
         yield ['fb.1.1656874832584.1088522659a'];