PayPal IPN

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:

1. User leaves client site and goes to PayPal.com to complete the transaction
2. User completes the transaction
3. PayPal's servers send a request directly to the PayPal IPN URL from PayPal's servers to the client's servers
4. Client'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 customer web site. As such 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.