Thanks so much.
I found that the session name was 'CustomerCart_OrderID'
So I changed the session and unset session to that name on the success page and everything works as expected.
<?php
if (!session_id()) session_start();
if(!isset($_SESSION["CustomerCart_OrderID"])) {
$_SESSION["CustomerCart_OrderID"] = "";
}
?>
<?php
$CustomerCart->ClearCart();
unset($_SESSION['CustomerCart_OrderID']);
?>
I appreciate the time you spent helping.
Cheers, Paul