When I test with my payment gateway (Sage Pay) I get a server error stating Craft Commerce isn't providing a redirect after payment is received:
Server error 5006: Unable to redirect to Vendor's web site. The Vendor failed to provide a RedirectionURL.
This is what is shown in my error logs:
220.127.116.11 - - [20/Jul/2016:09:05:17 +0100] "POST /index.php/actions/commerce/payments/completePayment?commerceTransactionId=9&commerceTransactionHash=b965d6bb8ca17ffc475849ab878721d5 HTTP/1.1" 404 50171 "-" "SagePay-Notifier/1.0"
Does anyone know what might be causing the redirect issue?