Hey, there!
@konrad.sopala could you please provide any update in this?
I’m also experiencing the same issue.
Despite using PreUserRegistrationError the error I get on the client side is generic:
{"name":"InternalExtensibilityError","statusCode":400,"code":"extensibility_error","message":"Extensibility error","description":"Extensibility error","fromSandbox":true}
Right now there is no way to understand on the client side what exactly is going on and handle error appropriately.
Tenant is configured to use New Universal Login Experience.
We are also using custom login and sign up pages