This is the payment response password from your WorldPay account.<br/>1. Log in to the Merchant Interface.<br/>2. Select 'Installations' from the left hand navigation.<br/>3. Choose an installation and select the 'Integration Setup' button for either the TEST or PRODUCTION environment.<br/>4. Enter a password into the 'Payment Response Password' input field.<br/>5. Check the 'Enable Payment Response' checkbox.<br/>6. Enter '&lt;wpdisplay item=MC_callback&gt;' into the 'Payment Response URL' input field.<br/>7. Select the 'Save Changes' button.