I have set up my payment page using checkout.js. Test payments seem to be working fine. Customers can only buy one product, so it is an extremely simple setup. Once the customer makes the payment, I need an IPN to trigger a simple database task that I have ready. I am probably doing it wrong, but wanted to track the user with a $SESSION['EmailAddress'] var...but this is not working out for me, lol. What is the correct approach to this very simple task?