jrockfl - 11:12 pm on Nov 13, 2012 (gmt 0)
For our e-commerce web site, when a user selects PayPal at checkout, I create a url that has special query string parameters and then the user is redirected to the PayPal web site.
Once they successfully complete the transaction, I use IPN (Instant Payment Notification) that processes a http post from PayPal.
This is how I know the user has successfully paid. The user is then redirected back to the e-commerce web site and a receipt is displayed.
Does that help?