PayPal Hacks

Chapter 7. IPN and PDT

Introduction: Hacks #65-86

One of the questions asked most often by merchants considering PayPal as a payment processor is, “How will I know when the customer pays?” If a merchant is employing any sort of automation or digital fulfillment, the question becomes, “How will my site know when the customer pays?” Obviously, since customers must leave your site to complete payment at the PayPal web site, your site (or its database) won’t know when your customer has paid until it has been notified by PayPal.

To that end, PayPal has developed two technologies for developers: Instant Payment Notification (IPN) and Payment Data Transfer (PDT). These technologies notify the merchant’s web server when payment has been attempted, whether or not it was successful, and details about the sale.

What IPN and PDT Are

Instant Payment Notification (IPN) is a means by which PayPal contacts your server directly every time a transaction completes; in other words, IPN is a call-back routine and part of an asynchronous process (in that the notification can happen any time after the transaction). This design has its benefits, such as accommodating eChecks that can take three to four days to process.

Payment Data Transfer (PDT), on the other hand, is fueled directly by your customer’s actions. First, you enable PayPal’s Auto Return feature, such that when a payment is completed, the customer is immediately returned to your site, along with some transaction information. Restricting the navigation ...