IPN is a service provided by PayPal that automatically notifies your server the instant a transaction occurs. This lets us ensure that all successful payments get marked as "paid" in our Form Tools database.
And here's the other piece of good news: you don't really need to know how it works. The zipfile contains a file with all the functions needed to interact with PayPal to confirm a purchase and mark the submission as complete. So... let's get started setting up your form!