The parameter, "Relay Response Hash" has been renamed as the "Relay Response Key" to avoid confusing it with other hash parameters. Whereas previously the Relay Response Key was a value chosen by the developer or merchant and entered into the "Relay Response" tab on the Administrative Console in Payeezy Gateway Real-time Payment Manager (RPM), it is now generated as part of the Payeezy Gateway Payment Page configuration on the "Security" tab.
To see the key, go to the Payeezy Gateway Payment Page configuration in the Real-time Payment Manager (RPM) and select the "Security" tab from the left side of the page. Create a new key by pressing the "Generate New Response Key" button. Note that re-generating the response key may interfere with any Relay Response process currently integrated for your Payeezy Gateway Payment Page.