How do I add an automatic thank you note once payment is submitted?

All forms should have a default THANK YOU PAGE that you can fully customize. You can either change the thank you message itself, or redirect them to your own preferred URL.

If your only goal is to setup your own thank you message after they submit your form, the guide below should help.

Complete guide: Setting-up-the-Thank-You-Page

In case we misunderstood, kindly get back to us with more info and a better description of what you're trying to achieve so we can better assist you.