Signup form displays irrelevant error message, although Signup form is disabled in Identities

Bug description
After customizing the Developer Portal by removing the Sign Up form, the form displays irrelevant error message than in dev tools

Both Sign Up button in Portal UI & Username, Password form with APIM Managed Identities has been removed.

Reproduction steps
Go APIM Developer Portal, remove Signup links
Go APIM -- Managed Identities - Delete Username, Password Identity
Save and Publish,
Go the Developer site in Incognito. Try Signup forma and feed relevant info,
Sign Up says no error in UI, though Developer Tool says - message: "User registration is not supported."

Expected behavior
Sign Up action should display relevant error message i.e User registration is not supported.

Is your portal managed or self-hosted?
Managed

API Management service name
ot-shared-apimgmt

Environment
Operating system: Any
Browser: Any
Version: Any[](url

)

Reproduce the disabled-signup flow in the managed Developer Portal after removing the Sign Up links and the Username, Password identity. Start by locating the signup UI flow from the portal entry points; done means the UI displays "User registration is not supported" instead of leaving the error only in developer tools.

Written by the indexing model from the issue text.