the code you sent in the checkout zip was the cart object code, not the checkout page cpde.
take the checkout.php page and compress it into a zip file please, do not copy and paste the code into a text file.
for the shipping issue, I need you to add the full request binding and the full response binding to the failure page, then run a test that will cause the failure page to display in the browser.
this should now show the full request and full response details on the failure page.
I need you to copy that information and paste it into your reply.
Before you hit the send button, you should edit out any sensitive information.