Handle: trying to reuse a code after it has already been used
Currently, when you try to reuse a code that’s already been used, you are not given any feedback and the flow gets stuck at that point as you’re not allowed to submit the form.
The reply area should check as the code is being entered and give you feedback if the code as has already been used. The Send button should only activate if a valid, unused code is entered. (See https://indienet.info/hallo.gent/#step-1-check-authorisation-for-free-domain)