How to block free emails from submitting a form?

Hey guys, how do you set up Wix forms so free/personal emails won’t be able to submit the form? I’ve been trying to do this for the longest time but for the life of me couldn’t find where this is. Appreciate the help!

This will help - Wix Functions: Adding Custom Validations to Your Forms | Help Center | Wix.com

This is definitely what I need! But it doesn’t look like it’s working for old Wix Forms. Any ideas how?

For old form you will need velo