eCart uses the POST method to send the transaction to WorlPay.
the action of the form on the confirm page is to post to "https://select.worldpay.com/wcc/purchase"
<form name="checkout_WP_CmpHid" action="https://select.worldpay.com/wcc/purchase" method="post">
you will need to edit that to post to "https://secure.worldpay.com/wcc/purchase" instead:
<form name="checkout_WP_CmpHid" action="https://secure.worldpay.com/wcc/purchase" method="post">