I'm doing a project involving Paypal, more specifically with the NVP API in PHP. But I just can't seem to figure what to use the IPN feature for.
I mean, when the user has been redirected to Paypal to confirm the purchase, he is redirected back to my website's "Paypal-succes-page", when the transaction is complete. And just to be sure that he actually payed i could use the "PaymentDetails" operation.
Now where does IPN fit in this process? and what is the benefit of it?
Thanks
The integrate with PayPal's services you will notice there are three main channels (and IMO it's important to know this so you can decide the benefits for your application):
To use PayPal's IPN you need to add a 'listener' script (example) and add the address to your PayPal account. Whenever an event occurs PayPal will send a message directly to your server via your listener and you then update your accounts appropriately. This is especially useful for running subscription services as events will occur in the background without user intervention and you can capture successful/failed recurring payments etc.
PayPal's PDT is a system for accepting data when a user is redirected back to your site from PayPal. For example, a user clicks 'Buy', they are directed to PayPal, enter information etc. Then, once the payment has been taken, they are redirected back to your site. PayPal can pass details about the transaction including whether it was successful or not so you can display the appropriate success/failed page from your site.
PayPal's API allows you to integrate more deeply with PayPal's services, and you would use this if you were managing payments directly from your site.
These services aren't mutually exclusive, so you can use any combination with your application.
I hope this helps
Instant Payment Notification
The typical usage of the IPN is to validate the purchase and to let your script or management system know that the transaction is complete so your system can update any records you may have for your service.
But the most important part is that the transaction is validated.
IPN send all data about transaction to your server - price, items, contacts ... so you can check, if someone don't pay you only 1$ instead of 100$ and confirm your order. It prevets thiefs, cheaters, ... USE IT! ;)
The IPN feature is a very useful feature which you should use to update your database in my opinion. Sure the user is redirected to your success-page after the purchase where you can validate the payment details.
But what if he closes (by accident or not) the browser before reaching your success page? You will never know the result of the transaction and you will never update your database or process his order accordingly.
When using the IPN you can be sure that the transaction result will always reach you because PayPal will keep on making an offline request to your IPN page until it has reached your servers.