Hi,
Thanks for getting back
I currently use the Form sagepay version on our live site, where all card processing is done on their secure site.
I asked whether your extension would be ok.
This is their reply -
Your shopping cart Abantecart should have a defect (i think they mean default?) a success or failure url where you and customers are notified of the order. You will need to speak with them to query this a little more.
Currently, if something goes wrong, customers are returned to an success/error url on our site, and we get a succes or failure email, and they need the url for their settings.