Your form will not validate because the form action is pointing at confirm.php, consequently the form values are passed directly to confirm.php bypassing your current validation.
You can solve this by validating your ecart_checkout_form form on your confirm.php page. To do this you need to expose the ecart_checkout_form values on confirm.php and you do this by using the Form Data option under Bindings and choose checkout.php as the page where the post is coming from then you can open up validation toolkit server behaviour as normal.
One tip make sure that on error you transfer back to checkout.php and have your error messages there rather than on confirm.php.