I just wanted to check in and see if you had any other questions or if you were able to resolve this issue?
After reviewing the Configure a custom domain for Azure Web PubSub Service documentation, it looks like you did everything correctly. However, please keep in mind that there might be a delay when an Access Policy is created to when it takes effect.
Note: It can take several hours for changes to a managed identity's group or role membership to take effect.
- For more info - Role assignment changes are not being detected.
If you're still having issues, can you share a screenshot of the full error message along with any documentation that you're following.
Thank you for your time and patience throughout this issue.