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navaldesign · #5 09-09-2008, 05:48 PM

IPN = Instant Payment Notification.

In other words, whenever a transaction is done in your PayPal account, Paypal sends the transaction details back to you, using the POST method (which means that the info is sent to your site just as if it was submitted through a form). Using them or not depends on you. If you have a script that can receive this info, you can do whatever you like with it.

In example, if you have a simple mailing script in the notification_url, the script can mail you all the details of the transaction, like the payers address, email, name and surname, the transaction ID, and much more.
This is the simplest way to use IPN.
A more complete script would use these details, to "activate" an order, to store the info in the database, and most important, to verify with PayPal the authenticity of the info received (which is acheived re-sending the info to PayPal and requesting a verification- Then PayPal answers back through yet another communication, with a False or True answer). This becomes ABSOLUTELY necesary when there are downloadable products that you want to allow instant download after payment.

IPN has no visual output, the entire process is invisible to the user, as it is a communication between the script on your site and PayPal. However, the actions taken by the script (in example activating a membership account, or renewing it, or enabling a product download, or updating a database with the customers details or other) can affect, in a dynamic environment, the way that the site will behave towards a user that has made the payment.

My Cart, my Instant Download Cart and my Customized Logger (membership script) use IPN exactly for the above purposes. However, since IPN informs you of ANY transaction, you can use it also for cancellations and pre-payment authorizations.