We require a payment gateway to be coded for WHMCS for First Data's API integration.
The user will enter their card details into the WHMCS credit card form, the details will submit to the gateway and the customer will stay on our site and be redirected to 3D secure where appropriate and then return to the invoice page to show they've paid, or return an error on the credit card page stating the payment was declined.
Card details will not be stored in WHMCS or tokenised, so the coding will be fairly straight forward.
The integration guide is here: [url removed, login to view]
Sample code here: [url removed, login to view]