diff --git a/src/backend/src/controllers/users.controllers.ts b/src/backend/src/controllers/users.controllers.ts
index 75fe877002..00e1f637b1 100644
--- a/src/backend/src/controllers/users.controllers.ts
+++ b/src/backend/src/controllers/users.controllers.ts
@@ -242,4 +242,14 @@ export default class UsersController {
       next(error);
     }
   }
+
+  static async validateSlackId(req: Request, res: Response, next: NextFunction) {
+    try {
+      const { slackId } = req.body;
+      const isValid = await UsersService.validateSlackId(slackId);
+      res.status(200).json({ isValid });
+    } catch (error: unknown) {
+      next(error);
+    }
+  }
 }
diff --git a/src/backend/src/integrations/slack.ts b/src/backend/src/integrations/slack.ts
index 0ac331f125..9ecde09c57 100644
--- a/src/backend/src/integrations/slack.ts
+++ b/src/backend/src/integrations/slack.ts
@@ -289,7 +289,7 @@ export const checkBotInChannel = async (channelId: string): Promise<boolean> =>
 };
 
 /**
- * Given a slack user id, prood.uces the name of the channel
+ * Given a slack user id, produces the name of the channel
  * @param userId the id of the slack user
  * @returns the name of the user (real name if no display name), undefined if cannot be found
  */
@@ -380,3 +380,20 @@ export const getReceiver = (): ExpressReceiver | null => {
 // Export the getters for any direct usage if needed
 export { getSlackClient };
 export default getSlackClient;
+
+/**
+ * Validates that a given Slack user id exists in the workspace
+ * All slack ids start with U. If you pass a valid user id to users.info, it returns ok: true; throws error otherwise.
+ * @param slackId the Slack user id to validate
+ * @returns true if the user exists, false otherwise
+ */
+export const validateSlackUserId = async (slackId: string): Promise<boolean> => {
+  const client = getSlackClient();
+  if (!client) return false;
+  try {
+    const res = await client.users.info({ user: slackId });
+    return res.ok === true;
+  } catch (error) {
+    return false;
+  }
+};
diff --git a/src/backend/src/routes/users.routes.ts b/src/backend/src/routes/users.routes.ts
index 98a7b6b21f..11cba8d7ee 100644
--- a/src/backend/src/routes/users.routes.ts
+++ b/src/backend/src/routes/users.routes.ts
@@ -66,4 +66,6 @@ userRouter.post(
   UsersController.getManyUserTasks
 );
 
+userRouter.post('/validate-slack-id', nonEmptyString(body('slackId')), validateInputs, UsersController.validateSlackId);
+
 export default userRouter;
diff --git a/src/backend/src/services/users.services.ts b/src/backend/src/services/users.services.ts
index 69bf4cf9e5..bce2daf453 100644
--- a/src/backend/src/services/users.services.ts
+++ b/src/backend/src/services/users.services.ts
@@ -29,6 +29,7 @@ import authenticatedUserTransformer from '../transformers/auth-user.transformer.
 import { getTaskQueryArgs } from '../prisma-query-args/tasks.query-args.js';
 import taskTransformer from '../transformers/tasks.transformer.js';
 import { validateUserIsPartOfFinanceTeamOrHead } from '../utils/reimbursement-requests.utils.js';
+import { validateSlackUserId } from '../integrations/slack.js';
 
 export default class UsersService {
   /**
@@ -622,4 +623,13 @@ export default class UsersService {
 
     return users.map(userWithScheduleSettingsTransformer);
   }
+
+  /**
+   * Validates a user's slack id
+   * @param slackId the Slack user id to validate
+   * @returns true if the user exists, false otherwise
+   */
+  static async validateSlackId(slackId: string): Promise<boolean> {
+    return validateSlackUserId(slackId);
+  }
 }
diff --git a/src/backend/tests/unit/users.test.ts b/src/backend/tests/unit/users.test.ts
index 0c532f579e..2896c38473 100644
--- a/src/backend/tests/unit/users.test.ts
+++ b/src/backend/tests/unit/users.test.ts
@@ -10,6 +10,12 @@ import {
 import UsersService from '../../src/services/users.services.js';
 import { NotFoundException, AccessDeniedException } from '../../src/utils/errors.utils.js';
 import { RoleEnum } from 'shared';
+import { vi, Mock } from 'vitest';
+import * as slackIntegration from '../../src/integrations/slack.js';
+
+vi.mock('../../src/integrations/slack.js', () => ({
+  validateSlackUserId: vi.fn()
+}));
 
 describe('User Tests', () => {
   let orgId: string;
@@ -119,4 +125,24 @@ describe('User Tests', () => {
       ).rejects.toThrow(new AccessDeniedException('Guests and members cannot update user roles!'));
     });
   });
+
+  describe('Validate Slack id tests', () => {
+    it('returns true for a valid Slack id', async () => {
+      (slackIntegration.validateSlackUserId as Mock).mockResolvedValue(true);
+      const result = await UsersService.validateSlackId('U06D5RURPMF');
+      expect(result).toBe(true);
+    });
+
+    it('returns false for an invalid Slack id', async () => {
+      (slackIntegration.validateSlackUserId as Mock).mockResolvedValue(false);
+      const result = await UsersService.validateSlackId('BLAH');
+      expect(result).toBe(false);
+    });
+
+    it('returns false when Slack client is not configured', async () => {
+      (slackIntegration.validateSlackUserId as Mock).mockResolvedValue(false);
+      const result = await UsersService.validateSlackId('U06D5RURPMF');
+      expect(result).toBe(false);
+    });
+  });
 });
diff --git a/src/frontend/src/apis/users.api.ts b/src/frontend/src/apis/users.api.ts
index 4da38b9489..bb0292e847 100644
--- a/src/frontend/src/apis/users.api.ts
+++ b/src/frontend/src/apis/users.api.ts
@@ -212,3 +212,13 @@ export const getManyUsersWithScheduleSettings = (userIds: string[]) => {
 export const logUserOut = () => {
   return axios.post<{ message: string }>(apiUrls.logUserOut());
 };
+
+/**
+ * Validates a user's slack id
+ *
+ * @param slackId the user's slack id
+ * @returns true if the slack id is valid, false otherwise
+ */
+export const validateSlackId = (slackId: string) => {
+  return axios.post<{ isValid: boolean }>(apiUrls.validateSlackId(), { slackId });
+};
diff --git a/src/frontend/src/app/AppAuthenticated.tsx b/src/frontend/src/app/AppAuthenticated.tsx
index f4228acb34..5b322ea7a4 100644
--- a/src/frontend/src/app/AppAuthenticated.tsx
+++ b/src/frontend/src/app/AppAuthenticated.tsx
@@ -37,9 +37,10 @@ import SidebarLayout from '../layouts/SidebarLayout';
 interface AppAuthenticatedProps {
   userId: string;
   userRole: Role;
+  completedOnboarding: boolean;
 }
 
-const AppAuthenticated: React.FC<AppAuthenticatedProps> = ({ userId, userRole }) => {
+const AppAuthenticated: React.FC<AppAuthenticatedProps> = ({ userId, userRole, completedOnboarding }) => {
   const { isLoading, isError, error, data: userSettingsData } = useSingleUserSettings(userId);
 
   const {
@@ -64,7 +65,7 @@ const AppAuthenticated: React.FC<AppAuthenticatedProps> = ({ userId, userRole })
 
   return (
     <GlobalCarFilterProvider>
-      {userSettingsData.slackId || isGuest(userRole) ? (
+      {userSettingsData.slackId || (isGuest(userRole) && !completedOnboarding) ? (
         <AppContextUser>
           <SidebarLayout>
             <Switch>
diff --git a/src/frontend/src/app/AppPublic.tsx b/src/frontend/src/app/AppPublic.tsx
index 0591137c0e..e9be388e0c 100644
--- a/src/frontend/src/app/AppPublic.tsx
+++ b/src/frontend/src/app/AppPublic.tsx
@@ -34,7 +34,12 @@ const AppPublic: React.FC = () => {
         return <LoadingIndicator />;
       }
 
-      return <AppAuthenticated userId={auth.user.userId} userRole={auth.user.role} />;
+      //get onboarding completion to pass to authenticated app for routing
+      const completedOnboarding = auth.user.onboardedTeamTypeIds.length > 0;
+
+      return (
+        <AppAuthenticated userId={auth.user.userId} userRole={auth.user.role} completedOnboarding={completedOnboarding} />
+      );
     }
 
     if (!auth.user && !auth.triedCurrent) {
diff --git a/src/frontend/src/hooks/users.hooks.ts b/src/frontend/src/hooks/users.hooks.ts
index c890c23671..ffb3eb19bd 100644
--- a/src/frontend/src/hooks/users.hooks.ts
+++ b/src/frontend/src/hooks/users.hooks.ts
@@ -24,7 +24,8 @@ import {
   logUserOut,
   getManyUsersWithScheduleSettings,
   getAllOrgUsers,
-  getAllOrgMembers
+  getAllOrgMembers,
+  validateSlackId
 } from '../apis/users.api';
 import {
   User,
@@ -322,3 +323,13 @@ export const useLogUserOut = () => {
     return data;
   });
 };
+
+/**
+ * Custom react hook to determine if a user's slack id is valid
+ */
+export const useValidateSlackId = () => {
+  return useMutation<{ isValid: boolean }, Error, string>(['users', 'validate-slack-id'], async (slackId: string) => {
+    const { data } = await validateSlackId(slackId);
+    return data;
+  });
+};
diff --git a/src/frontend/src/pages/AcceptedPage/AcceptedPage.tsx b/src/frontend/src/pages/AcceptedPage/AcceptedPage.tsx
deleted file mode 100644
index ffc1848737..0000000000
--- a/src/frontend/src/pages/AcceptedPage/AcceptedPage.tsx
+++ /dev/null
@@ -1,86 +0,0 @@
-import { Typography, Box, Grid } from '@mui/material';
-import PageLayout from '../../components/PageLayout';
-import { NERButton } from '../../components/NERButton';
-import { useHistory } from 'react-router-dom';
-import { useCurrentUser } from '../../hooks/users.hooks';
-import { routes } from '../../utils/routes';
-import { useCompleteOnboarding } from '../../hooks/team-types.hooks';
-import LoadingIndicator from '../../components/LoadingIndicator';
-import { useCurrentOrganization } from '../../hooks/organizations.hooks';
-
-const AcceptedPage = () => {
-  const history = useHistory();
-  const user = useCurrentUser();
-  const { data: organization, isLoading: organizationIsLoading } = useCurrentOrganization();
-
-  const { mutateAsync: completeOnboarding, isLoading: completeOnboardingIsLoading } = useCompleteOnboarding();
-
-  if (completeOnboardingIsLoading || !organization || organizationIsLoading) {
-    return <LoadingIndicator />;
-  }
-
-  const handleClick = async () => {
-    await completeOnboarding();
-    window.location.reload();
-  };
-
-  return (
-    <PageLayout title="Accepted" hidePageTitle>
-      <Box sx={{ mt: 6, ml: 4 }}>
-        <Typography variant="h2" marginLeft="auto" sx={{ marginTop: 2, textAlign: 'center', pt: 3, padding: 0 }}>
-          Congratulations, {user.firstName}!
-        </Typography>
-        <Typography
-          variant="h3"
-          marginLeft="auto"
-          sx={{ marginTop: 2, textAlign: 'center', pt: 1, padding: 0, fontWeight: 1 }}
-        >
-          We are so excited to welcome you to {organization.name}!
-        </Typography>
-      </Box>
-      <Box
-        component="img"
-        src={'../NER-Logo-App-Icon.png'}
-        sx={{
-          width: '25%',
-          height: '25%',
-          display: 'block',
-          marginLeft: 'auto',
-          marginRight: 'auto',
-          marginTop: 4
-        }}
-      />
-      <Box sx={{ mt: 2, ml: 2 }}>
-        <Typography
-          variant="h6"
-          marginLeft="auto"
-          sx={{ marginTop: 1, textAlign: 'center', pt: 3, padding: 0, fontFamily: 'oswald', fontWeight: 1, fontSize: 25 }}
-        >
-          We can't wait to see you around and all that you'll accomplish!
-        </Typography>
-      </Box>
-      <Box
-        sx={{
-          display: 'flex',
-          justifyContent: 'center',
-          mt: 7,
-          width: '100%'
-        }}
-      >
-        <Grid container justifyContent="center" spacing={8} sx={{ maxWidth: '500px' }}>
-          <Grid item>
-            <NERButton variant="contained" sx={{ fontSize: 20 }} onClick={() => history.push(routes.HOME_SELECT_SUBTEAM)}>
-              Reject
-            </NERButton>
-          </Grid>
-          <Grid item>
-            <NERButton variant="contained" sx={{ fontSize: 20 }} onClick={handleClick}>
-              Accept
-            </NERButton>
-          </Grid>
-        </Grid>
-      </Box>
-    </PageLayout>
-  );
-};
-export default AcceptedPage;
diff --git a/src/frontend/src/pages/HomePage/Home.tsx b/src/frontend/src/pages/HomePage/Home.tsx
index 7439241e4a..e2aa183cdb 100644
--- a/src/frontend/src/pages/HomePage/Home.tsx
+++ b/src/frontend/src/pages/HomePage/Home.tsx
@@ -7,7 +7,6 @@ import { routes } from '../../utils/routes';
 import PNMHomePage from './PNMHomePage';
 import OnboardingHomePage from './OnboardingHomePage';
 import SelectSubteamPage from './SelectSubteamPage';
-import AcceptedPage from '../AcceptedPage/AcceptedPage';
 import HomePage from './HomePage';
 import { useCurrentUser } from '../../hooks/users.hooks';
 import IntroGuestHomePage from './IntroGuestHomePage';
@@ -23,12 +22,9 @@ const Home: React.FC = () => {
     <Switch>
       {completedOnboarding &&
         !isAdmin(user.role) &&
-        [routes.HOME_PNM, routes.HOME_ONBOARDING, routes.HOME_ACCEPT].map((path) => (
-          <Redirect exact path={path} to={routes.HOME} />
-        ))}
+        [routes.HOME_PNM, routes.HOME_ONBOARDING].map((path) => <Redirect exact path={path} to={routes.HOME} />)}
       {onOnboarding && !completedOnboarding && <Redirect exact path={routes.HOME} to={routes.HOME_PNM} />}
       <Route exact path={routes.HOME_SELECT_SUBTEAM} component={SelectSubteamPage} />
-      <Route exact path={routes.HOME_ACCEPT} component={AcceptedPage} />
       <Route exact path={routes.HOME_ONBOARDING} component={OnboardingHomePage} />
       <Route exact path={routes.HOME_PNM} component={PNMHomePage} />
       <Route exact path={routes.HOME_MEMBER} component={HomePage} />
diff --git a/src/frontend/src/pages/HomePage/OnboardingHomePage.tsx b/src/frontend/src/pages/HomePage/OnboardingHomePage.tsx
index 7f6b9836a9..25a23ca79f 100644
--- a/src/frontend/src/pages/HomePage/OnboardingHomePage.tsx
+++ b/src/frontend/src/pages/HomePage/OnboardingHomePage.tsx
@@ -13,6 +13,7 @@ import { routes } from '../../utils/routes';
 import { useCurrentOrganization } from '../../hooks/organizations.hooks';
 import OnboardingProgressBar from '../../components/OnboardingProgressBar';
 import ErrorPage from '../ErrorPage';
+import { useCompleteOnboarding } from '../../hooks/team-types.hooks';
 
 const OnboardingHomePage = () => {
   const history = useHistory();
@@ -41,6 +42,8 @@ const OnboardingHomePage = () => {
 
   const progress = useChecklistProgress(usersChecklists || [], checkedChecklists || []);
 
+  const { mutateAsync: completeOnboarding } = useCompleteOnboarding();
+
   if (usersChecklistsIsError) {
     return <ErrorPage error={usersChecklistsError} />;
   }
@@ -69,7 +72,8 @@ const OnboardingHomePage = () => {
   };
 
   const handleConfirmModal = async () => {
-    history.push(routes.HOME_ACCEPT);
+    await completeOnboarding();
+    history.push(routes.HOME);
   };
 
   return (
diff --git a/src/frontend/src/pages/HomePage/components/SetUserPreferences.tsx b/src/frontend/src/pages/HomePage/components/SetUserPreferences.tsx
index 74292b5dfd..11634e4805 100644
--- a/src/frontend/src/pages/HomePage/components/SetUserPreferences.tsx
+++ b/src/frontend/src/pages/HomePage/components/SetUserPreferences.tsx
@@ -15,7 +15,7 @@ import LoadingIndicator from '../../../components/LoadingIndicator';
 import NERSuccessButton from '../../../components/NERSuccessButton';
 import ReactHookTextField from '../../../components/ReactHookTextField';
 import { useToast } from '../../../hooks/toasts.hooks';
-import { useUpdateUserSettings } from '../../../hooks/users.hooks';
+import { useUpdateUserSettings, useValidateSlackId } from '../../../hooks/users.hooks';
 import ErrorPage from '../../ErrorPage';
 
 interface SetUserPreferencesProps {
@@ -28,13 +28,20 @@ const SetUserPreferences: React.FC<SetUserPreferencesProps> = ({ userSettings })
   const { handleSubmit, control } = useForm<{ slackId: string }>({
     defaultValues: { slackId: userSettings.slackId }
   });
+  const { mutateAsync: validateSlackId } = useValidateSlackId();
 
   if (isLoading) return <LoadingIndicator />;
   if (isError) return <ErrorPage message={error?.message} />;
 
   const onSubmit = async ({ slackId }: { slackId: string }) => {
     try {
+      const { isValid } = await validateSlackId(slackId);
+      if (!isValid) {
+        toast.error('Invalid Slack ID! Please check it and try again.');
+        return;
+      }
       await mutateAsync({ ...userSettings, slackId });
+      // window.location.reload(); might not need this if it rerenders automatically
     } catch (error: unknown) {
       if (error instanceof Error) {
         toast.error(error.message);
diff --git a/src/frontend/src/tests/app/AppAuthenticated.test.tsx b/src/frontend/src/tests/app/AppAuthenticated.test.tsx
index 33d961cbb4..0d38fc4b11 100644
--- a/src/frontend/src/tests/app/AppAuthenticated.test.tsx
+++ b/src/frontend/src/tests/app/AppAuthenticated.test.tsx
@@ -30,7 +30,7 @@ const renderComponent = (path?: string, route?: string) => {
   const RouterWrapper = routerWrapperBuilder({ path, route });
   return render(
     <RouterWrapper>
-      <AppAuthenticated userId={'1'} userRole={'GUEST'} />
+      <AppAuthenticated userId={'1'} userRole={'GUEST'} completedOnboarding={false} />
     </RouterWrapper>
   );
 };
diff --git a/src/frontend/src/utils/routes.ts b/src/frontend/src/utils/routes.ts
index ce658120bd..bd4b941769 100644
--- a/src/frontend/src/utils/routes.ts
+++ b/src/frontend/src/utils/routes.ts
@@ -15,7 +15,6 @@ const CREDITS = `/credits`;
 const HOME = `/home`;
 const HOME_PNM = HOME + `/pnm`;
 const HOME_SELECT_SUBTEAM = HOME + `/select-subteam`;
-const HOME_ACCEPT = HOME + `/accept`;
 const HOME_MEMBER = HOME + `/member`;
 const HOME_ONBOARDING = HOME + `/onboarding`;
 
@@ -93,7 +92,6 @@ export const routes = {
   HOME_PNM,
   HOME_SELECT_SUBTEAM,
   HOME_ONBOARDING,
-  HOME_ACCEPT,
   HOME_MEMBER,
 
   TEAMS,
diff --git a/src/frontend/src/utils/urls.ts b/src/frontend/src/utils/urls.ts
index ee39409179..609f913492 100644
--- a/src/frontend/src/utils/urls.ts
+++ b/src/frontend/src/utils/urls.ts
@@ -32,6 +32,7 @@ const manyUserTasks = () => `${users()}/tasks/get-many`;
 const currentUser = () => `${users()}/auth/current`;
 const logUserOut = () => `${users()}/auth/log-out`;
 const manyUsersWithScheduleSettings = () => `${users()}/scheduleSettings`;
+const validateSlackId = () => `${users()}/validate-slack-id`;
 
 /**************** Projects Endpoints ****************/
 const projects = () => `${API_URL}/projects`;
@@ -532,6 +533,7 @@ export const apiUrls = {
   currentUser,
   logUserOut,
   manyUsersWithScheduleSettings,
+  validateSlackId,
 
   projects,
   allProjectsGantt,