Instant Payment Notification (IPN) notifies Users Ultra PRO almost instantly about transaction events.
Although PayPal usually processes IPN messages immediately, IPN is not synchronized with actions on your website. Internet connectivity is not always 100% reliable and IPN messages can be lost or delayed
When a customer makes a payment to you or a payment is reversed or refunded, PayPal will post a notification to Users Ultra PRO at the URL you specified. Included in this notification will be all of your customer’s payment information (e.g. customer name, payment amount) as well as a piece of encrypted code.
After you have activated Instant Payment Notification, your server will be sent a notification every time you receive a payment, this notification will be sent as a hidden “FORM POST” to the URL you specified, and will include all of the payment information.
IMPORTANT: Users Ultra PRO will create the IPN URL on a per-transaction basis, in which case you don’t need to set it up in your profile Paypal Profile.