I understand that you have been experiencing issues with signing up with a custom database.
To help you better, could you please clarify if the issue happens after clicking the “sign up” button or does the login/signup page not load and return the error message?
Secondly, have you gotten a chance to use test the database scripts by pressing the Save and Try button?
This can happen when a function’s parameter gets assigned to a value that is not a member of the parameter’s defined set of acceptable values inside your database scripts.
With that, I recommend revising your database scripts again and testing them with the built-in “Save and Try” button. It may also be useful to include console.log() statements and debug with the Real-time Webtask Logs Extension.