diff --git a/checkout_sdk/payments/payments.py b/checkout_sdk/payments/payments.py
index 512e1b3..ce55532 100644
--- a/checkout_sdk/payments/payments.py
+++ b/checkout_sdk/payments/payments.py
@@ -623,17 +623,23 @@ class ProcessingSettings:
     scheme_transaction_link_id: str
 
 
-class ProductSubType (str, Enum):
-    BLOCKCHAIN = 'BLOCKCHAIN'
-    CBDC = 'CBDC'
-    CRYPTOCURRENCY = 'CRYPTOCURRENCY'
-    NFT = 'NFT'
-    STABLECOIN = 'STABLECOIN'
+class ItemType(str, Enum):
+    DIGITAL = 'digital'
+    DISCOUNT = 'discount'
+    PHYSICAL = 'physical'
+
+
+class ProductSubType(str, Enum):
+    BLOCKCHAIN = 'blockchain'
+    CBDC = 'cbdc'
+    CRYPTOCURRENCY = 'cryptocurrency'
+    NFT = 'nft'
+    STABLECOIN = 'stablecoin'
 
 
 class Product:
-    type: str
-    sub_type: list  # ProductSubType
+    type: ItemType = None
+    sub_type: ProductSubType = None
     name: str
     quantity: int
     unit_price: int
diff --git a/tests/payments/product_serialization_test.py b/tests/payments/product_serialization_test.py
new file mode 100644
index 0000000..8b8b446
--- /dev/null
+++ b/tests/payments/product_serialization_test.py
@@ -0,0 +1,97 @@
+import json
+
+from checkout_sdk.json_serializer import JsonSerializer
+from checkout_sdk.payments.payments import Product, ProductSubType, ItemType
+
+
+def _serialize(obj):
+    return json.loads(json.dumps(obj, cls=JsonSerializer))
+
+
+class TestProductSerialization:
+
+    def test_sub_type_serializes_as_lowercase(self):
+        p = Product()
+        p.sub_type = ProductSubType.BLOCKCHAIN
+        assert _serialize(p)['sub_type'] == 'blockchain'
+
+    def test_all_sub_type_values_serialize_lowercase(self):
+        expected = {
+            ProductSubType.BLOCKCHAIN: 'blockchain',
+            ProductSubType.CBDC: 'cbdc',
+            ProductSubType.CRYPTOCURRENCY: 'cryptocurrency',
+            ProductSubType.NFT: 'nft',
+            ProductSubType.STABLECOIN: 'stablecoin',
+        }
+        for enum_val, expected_str in expected.items():
+            p = Product()
+            p.sub_type = enum_val
+            assert _serialize(p)['sub_type'] == expected_str
+
+    def test_all_type_values_serialize_lowercase(self):
+        expected = {
+            ItemType.DIGITAL: 'digital',
+            ItemType.DISCOUNT: 'discount',
+            ItemType.PHYSICAL: 'physical',
+        }
+        for enum_val, expected_str in expected.items():
+            p = Product()
+            p.type = enum_val
+            assert _serialize(p)['type'] == expected_str
+
+    def test_unset_type_and_sub_type_serialize_as_null(self):
+        # With = None class-level defaults, unset fields serialize as null (not omitted)
+        p = Product()
+        p.name = 'Gold Necklace'
+        p.quantity = 1
+        result = _serialize(p)
+        assert result['type'] is None
+        assert result['sub_type'] is None
+
+    def test_type_and_sub_type_accept_none(self):
+        # Explicitly assigning None is valid and serializes as null
+        p = Product()
+        p.type = None
+        p.sub_type = None
+        p.name = 'Widget'
+        result = _serialize(p)
+        assert result.get('type') is None
+        assert result.get('sub_type') is None
+
+    def test_type_and_sub_type_round_trip(self):
+        p = Product()
+        p.type = ItemType.DIGITAL
+        p.sub_type = ProductSubType.STABLECOIN
+        p.name = 'USDC'
+        p.quantity = 1
+        p.unit_price = 10000
+        p.reference = '858818ac'
+        p.commodity_code = 'DEF123'
+        p.unit_of_measure = 'units'
+        p.total_amount = 10000
+        p.tax_amount = 1000
+        p.tax_rate = 2000
+        p.discount_amount = 500
+        p.wxpay_goods_id = '1001'
+        p.image_url = 'https://example.com/image.jpg'
+        p.url = 'https://example.com/product'
+        p.sku = 'SKU-001'
+
+        result = _serialize(p)
+
+        assert result['type'] == 'digital'
+        assert result['sub_type'] == 'stablecoin'
+        assert result['name'] == 'USDC'
+        assert result['quantity'] == 1
+        assert result['unit_price'] == 10000
+        assert result['reference'] == '858818ac'
+        assert result['commodity_code'] == 'DEF123'
+        assert result['unit_of_measure'] == 'units'
+        assert result['total_amount'] == 10000
+        assert result['tax_amount'] == 1000
+        assert result['tax_rate'] == 2000
+        assert result['discount_amount'] == 500
+        assert result['wxpay_goods_id'] == '1001'
+        assert result['image_url'] == 'https://example.com/image.jpg'
+        assert result['url'] == 'https://example.com/product'
+        assert result['sku'] == 'SKU-001'