Building a form where user enters a unique ID number

Hey everyone,

A client has a one-day event. Each customer will be given a unique ID number via a card they’re given upon entry. The QR code on the card will take them to a webflow page for them to register.

We’d like this form to have all the usual Name, email, location details etc, but we’d also like them to enter in their unique ID number.

There are only a finite amount of ID numbers. Obviously I can’t make sure that people enter in their ID number correctly, but how do I ensure that no two people enter in the same ID number. I’d like there to be an “error that ID number has been used” sort of message.

Let me know if anyone can help. If the answer is custom code, could you please let me know what sort of custom code and where to find resources?