Extensibility error - Pre User Registration

When a user tries to login I am getting the error Extensibility error.
Why does this happen?

This is the error
“name”: “InternalExtensibilityError”,
“statusCode”: 400,
“code”: “extensibility_error”,
“message”: “Extensibility error”,
“fromSandbox”: true

Hey there!

Can you provide us with more info so we can start debugging it? For now we simply lack details. Any screenshots or info about the stack you use etc. would be helpful!