A test shopper can be redirected to Worldpay server and complete the payment. I set up the www.yoursite.com/WorldpayPayment_Handler/paid/ as the callback URL in Worldpay, then the problem is callback doesn't seems working at all, it doesn't update the shopper's payment status and won't redirect the shopper back my site.
Does anyone have the similar problem? Or can anyone write a short instruction here about how to make the callback working?
I know this post was a year ago, but did you get this resolved? I am having the same issue - I've hardcoded the test status into WorldpayPayment.php and the test payments are fine, but at the end of the process nothing happens on the worldpay site to redirect back or update the order status. I have added http://thesitename.com/WorldpayPayment_Handler/paid/ as the callback and set the password up, but nothing.
Still working on this! I understand now that the site shouldn't redirect back - that makes sense. But the call back is not working either, as no status is updated. The error from Worldpay is: Error reported: Callback to: http://www.thesitename.com/worldpay/paid/: failed CAUSED BY invalid HTTP status line: >null<.