Thank you for your reply, I am keeping backup everytime I make changes based on your advice.
So as you mentioned, I emptied values for ID columns in Cart Summary and Cart Details wizard windows, except I kept OrderDetailsOrderID Value as;
<?php echo $_SESSION['Swift_OrderID']; ?>
I hope this is right, without filling this in the eCart5 doesn't let me finish the wizard. And the confirm.php page is now showing up as it's supposed to.
Unfortunately I have another problem though, which the "submit order" button is not functioning properly.
It should take me to checkout success page sending order detail to database, but instead, it stays the same confirmation.php page.
I have UE confirmation email redirecting to myself and customer, but at the moment the message only shows "0". At the same time, I noticed the "Universal Email" bit under Server Behavior panel is gone. (So I think I have to insert "Create Email message" server behavior again.)
It looks like now the category for this thread is shifting?
Should I change the category and create a new thread?