The parameter ReqID is used to prevent double payments by a customers, for example, if the back button is used in the browser. The ReqID is triggered by a proper check-out within the shop. If the transaction is resubmitted with the same ReqID, the Paygate does not execute a payment but only returns the status of the original transaction.
Note: Please note that the Paygate must have a completed transaction status for the first initial action. Submissions with identical ReqID to an open status are processed regularly.