Instant Payment Notifications (IPNs) will be fired when the merchant has provided a NotificationURL in the SetTransaction or DoTransaction API call under the following conditions:
When a payment on the PayU redirect either fails or succeeds.
When a user session times out on the PayU redirect with no chance for the user to finish payment.
When a transaction, pending review for fraud, is either approved or rejected by case managers. In the case of approval the IPN will fire after the payment has been attempted and will return that result.
The NotificationURL can be set to an HTTP or HTTPS endpoint. PayU will attempt to post the IPN 3 times with 1 minute intervals, failing which the IPN data will automatically be sent to the merchant as an email.