PayPal IPN (Instant Payment Notification) allows you to integrate your PayPal payments with your website’s back-end operations, so you get immediate notification and authentication of the PayPal payments you receive.
To enable PayPal IPN please follow the following steps:
http://your-doamin.com/?action=wpdmpp-payment-notification&class=Paypalfor that field.
For any technical issue, if you are already using pro version please post in pro forum and free version users please post in free forum. Otherwise, if you have any pre-sale or order related query please contact live chat support team. For technical support.