User Guide

IPN Guide June, 2009 17
Introducing IPN
Non-IPN Notification Mechanisms
PayPal will then send one single-word message, VERIFIED, if the message is valid; otherwise,
it will send another single-word message, INVALID.
IMPORTANT: After you receive the VERIFIED message, there are several important checks
you must perform before you can assume that the message is legitimate and
not already processed:
Confirm that the payment status is Completed.
Use the transaction ID to verify that the transaction has not already been
processed, which prevents duplicate transactions from being processed.
Validate that the receiver’s email address is registered to you.
Verify that the price, item description, and so on, match the transaction on
your website.
Non-IPN Notification Mechanisms
You can use IPN with other notification mechanisms. For example, you can use PDT or the
API to determine real-time information about a transaction and let IPN notify you of any
changes after the transaction occurs.
If you are using Website Payments Standard, you can use PDT to obtain information about the
transaction. If you are using Express Checkout or Direct Payment, the PayPal API notifies you
of the status and details of the transaction immediately and automatically. In either case, you
can immediately display to your customer the information being returned from PayPal. You
should not use IPN for this purpose.