Small businesses often rely on PayPal's email notifications or the Transaction History in their account to prepare items for shipping. Larger volume merchants, however, frequently need an automated process to record their sales and trigger fulfillment.

PayPal's Instant Payment Notification (IPN) allows you to integrate your PayPal payments with your website's back-end operations, so you get immediate notification and authentication of the PayPal payments you receive.

IPN makes it simple for large merchants to take advantage of PayPal's low fees and fraud protection while eliminating the need for manually transferring transaction data for shipping and fulfillment.

Click here for further instructions on using IPN as well as sample code.