There is an example for paypal IPN:

* [prepareAction](https://github.com/Payum/PayumBundleSandbox/blob/master/src/Acme/PaypalExpressCheckoutBundle/Controller/PurchaseExamplesController.php#L228).
* [StoreNotifactionAction](https://github.com/Payum/PayumBundleSandbox/blob/master/src/Acme/PaymentBundle/Payum/Action/StoreNotificationAction.php)