Hi,
As far as current error messages you should find most common ones here: https://auth0.com/docs/libraries/error-messages
And as a note, if you’d like to change what codes display to users, you can look into using Lock or the Hosted Login Page in the management UI which would give you control over how sign up and login messages display. See here for that: Customize Lock Error Messages
Let me know if there is any more I can advise.