Add the protx include file to the top of the checkout success page:
<?php
require_once("WA_eCart/checkoutScripts/Protx_VSPForm.php");
?>
make sure you have edited that file and put in your protx password in the first line.
Then change the triggers on lines 19 and 52 from:
if (isset($_POST["Payment_submit"]) || isset($_POST["Payment_submit_x"])) {
to:
if ($Protx_VSPServer_Profile['Success']) {