User Guide

Introducing IPN
A Sample IPN Message and Response
14 June, 2009 IPN Guide
The numbers in diagram correspond to the following steps, which implement the IPN message
authentication protocol:
1. PayPal sends your IPN listener a message that notifies you of the event
2. Your listener sends the complete unaltered message back to PayPal; the message must
contain the same fields in the same order and be encoded in the same way as the original
message
3. PayPal sends a single word back, which is either VERIFIED if the message originated with
PayPal or INVALID if there is any discrepancy with what was originally sent
After successfully completing the protocol, your back-office or administrative process vets the
contents of the message and responds appropriately. For example, the IPN messages may
trigger you to print shipping labels for items whose payments have cleared, investigate
disputes and chargebacks, store information in an accounting system, and so on.
A Sample IPN Message and Response
An IPN message consists of variables that describe the transaction. These variables contain
information about you, your customer, and the details of the transaction itself.
PayPal sends a message, similar to the following one, for a $19.95 purchase made by Express
Checkout: