Hi @paulatkins88 , welcome to the Auth0 Community!
Could you please confirm if my understanding is correct:
You have a certain deployment (it could be production or preview) that has assigned a custom domain on Vercel. So, when you try to log in, you are redirected back to the preview URL, and you get an error.
Additionally, if possible, could you please provide more details about the issue you’re experiencing? It would be helpful for any error messages or codes that are displayed.
Thank you!