How to enable SUBMIT to only work if payment has been made?

Hi,

I've created my form but trying to get details ironed out. We are signing up vendors for a festival and I want to avoid multiple submissions (i.e., testing it out, starting and not finishing).  My ideal situation is that they have PAID (submitted and payment processed through Paypal - already set up) OR no submission comes thru.

Is this possible?  Or is there a better way? 

Unfortunately its not possible to have form process payment first before user submits it. However what is possible is you can configure the payment field as required. This way user has to fill the payment field before the form is submitted otherwise form will not submit.

https://www.jotform.com/blog/254-Should-You-Use-Required-Fields-on-Your-Form

https://www.jotform.com/help/367-How-to-Make-a-Field-Required-Based-on-User-s-Answer

Kindly do let us know if the above resolves your issue.