Booking system: limit option to 1 choice

[Noemi_Van_Alsen]

I am trying to create a booking tool for oral examination. I managed to create a form where the student can select a hour of his/her choice (in a list) and when submitted, that time slot is no longer available for other students. So far so good.
But I noticed that students can add+ multiple slots; I would like this to be limited to 1. How can I fix this?
Additionally is there a way that students can only submit the form once?

[Kamille_Parks · Accepted solution]

If the field in question is a Link to Another Record field, make sure “Allow linking to multiple records” is turned off

[Noemi_Van_Alsen]

Thank you very much, problem solved!