Acronym. PayPal Instant Payment Notification. Technology from PayPal which notifies a host site immediately when an order is accepted or rejected. The flow of control is as follows:
- User leaves commerce site and goes to PayPal.com to complete the transaction
- User completes the transaction
- PayPal's servers send the transaction details directly to the PayPal IPN URL from PayPal's servers to the commerce site's servers
- Commerce site's IPN script records the transaction as completed
From the customer perspective, the PayPal IPN notification is "behind the scenes" and does not occur using the client's browser at all. It is a server-side connection from PayPal to the commerce web site. Because of this, customers must make considerations to preserve the customer identity to properly associate the sale with the original source of the sale.
See PayPal IPN for details on PayPal IPN.