One time view payment goes through but no validation is sent.

Hello,
I have setup Pay Per View to block a download link within the post content. The paywall appears, the user clicks and is taking to paypal to pay, unfortunately user returns back to the site and is given a "confirm payment to view content button" no instant access. Even when the user clicks on the button to "confirm" they are redirected back to the initial paywall. Throughout this payment is taken at the gateway, and once transaction is recorded on PPV after the confirm button, but no access is given. All API credentials have been setup correctly as well as the IPN url and the PDT token.

Please provide me with a solution,

Thanks,