Sign-up not completed error

My app has been rejected by App Store review because the sign in with Apple functionality is not working properly. I'm able to reproduce the issue on my end but I don't understand why it's happening.

I have two other apps that implement the same OAuth flow in an identical manner, and those apps have no issues signing in with Apple.

I've copied my OAuth flow to a fresh project to see if that would make a difference, and it gives me the exact same error. In the simulator I get "invalid_request, invalid web redirect URL", and on-device the FaceID authentication fails with a very non-specific "Sign Up Not Completed" error.

I'm completely out of ideas here, so any guidance would be appreciated. Thanks!

Sign-up not completed error
 
 
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