Bueno he encontrado esto en la RED esta en ingles pero es facil de entender y es como dice el compañero SebasBeta
Cita: Next, set your rm field/variable to "2" (this will tell Paypal API to autoredirect to your return url after the order and pass the order info in POST format)
You can view the response from Paypal by doing a var_dump($_POST) or print_r($_POST).
One of the important variables from the response is $_POST['payment_status'] which will tell you the outcome of the order. A successful transaction is 'Completed'. A transaction that requires verification from Paypal or from the merchant's side is 'Pending'.
Lastly, don't forget to specify 'invoice' on your Paypal field/request so you can update the status of your order. Something like:
mysql_query("UPDATE Orders SET status='{$_POST['payment_status']}' WHERE order_id='{$_POST['invoice']}'");
Les dejo el link de la documentación oficial de pagos recurrentes
https://www.x.com/developers/paypal/documentation-tools/paypal-code-samples#recurringpayments