RBS WorldPay (http://www.worldpay.us/) payment gateway integration is a Bank Hosted integration meaning the user is re-directed to a secure page hosted by WorldPay to submit their card details then returned to your site and the cart where a confirmation page is displayed.
To setup the cart to use WorldPay as the payment gateway do the following:
1. Go to the BuyNow module settings “Payment Gateway Setup” section and select “RBS WorldPay” as the payment gateway.
2. You will be prompted to enter the following field:
instId - This is a required field for the gateway. instId is your RBS WorldPay Installation ID assigned to you when you sign up for the WorldPay gateway account.
In order to have World Pay return to your site the following 3 settings on the world pay merchant interface that need to be set:
1. Click on this link to go to the merchant interface http://www.rbsworldpay.com/support/index.php?page=login&c=WW
2. Select “Business Gateway – Formerly WorldPay” and click go
3. Select test or production whichever one you are trying to setup
4. Login using your credentials
5. Click “Installations” on the left panel
6. Click the button under the “Integrations Setup” column for the account you want to setup
7. In the field titled “Payment Response URL” cut and paste the url from the shopping cart confirm page. The confirm page is the cart page with the process payment button, the page right before you go to WorldPay
8. Check the box titled “Payment Response enabled”
9. Check the box titled “Enable the Shopper Response”
10. Save your changes