Fix Joomla Checkout Failure

When shoppers hit “Proceed to checkout” on my custom-built Joomla e-shop, the system throws the following fatal error and halts the purchase flow:

exception 'Exception' with message 'Failed to checkout order' in /home/cleanbox/public_html/Libraries/ATnet/OrderClient/Index.php:158
…(full trace pasted above)

Because of this, none of the integrated payment methods—Credit/Debit Cards, PayPal, or Bank Transfer—can be completed. The problem appears only at the checkout step; browsing, cart building and every other storefront function work fine.

Here’s what I need from you:
• Inspect the PHP stack trace and underlying ATnet_* classes to pinpoint the root cause.
• Patch or refactor the offending code so the checkout form renders correctly and transactions reach the payment gateway without errors.
• Test end-to-end with each payment option to confirm orders are created, confirmations fire, and no new warnings surface in Joomla logs.

I will give you full access to a staging copy (FTP + Joomla admin + database). Once the fix is verified there, we’ll migrate it to production.

Please outline roughly how you plan to diagnose the issue, any ATnet or Joomla extensions you intend to touch, and an estimated timeframe for the patch.