
Originally Posted by
lat9
You can make a template-override version of /includes/templates/template_default/templates/tpl_checkout_one_default.php to re-arrange the various elements of that page and move the coupon/gift-voucher element before the payment information.
Since the credit-card information is sensitive, it's not passed back-and-forth between the data-entry page (checkout_one) and its associated confirmation page (checkout_one_confirmation) and the confirmation page is where the coupon/gv handling determines whether/not the information entered is valid.