The "ReqID" request parameter is used to prevent double payments by a customer, for example by the back button in the browser. If the transaction is submitted again with the same ReqID, Paygate does not execute a payment but only returns the status of the original transaction.
The function is automatically available and does not require any special activation.
Note: Please note that Paygate must have a completed transaction status for the first initial action. Submissions with identical ReqID on an open status (for example a not yet completed 3D Secure transaction) will be processed regularly.