I faced the same issue where everything was working smoothly at first. However, once I allowed usernames, the problem started occurring.

Cause of the Issue: When allowing usernames in Clerk, the sign-up process expects a username to be provided. If it's missing, Clerk marks the user creation as incomplete, resulting in the following error:

{ "status": "missing_requirements", "missingFields": ["username"] }

if you are not using it turn it offenter image description here