User Manager documentation says an inactive user is created when a user submits the sign-up form for a new account. The user id does not become active until payment is successfully made. But if payment fails to complete, or the sequence is interrupted by disconnection, power outage, coding error, configuration error, etc., the chosen user ID can never be used again ("cannot create inactive user: such username already exists").

How do you manually clear out inactive users that you know are never going to become active so those IDs can be reused?