I do not see X-Payments connected payment method at your X-Cart site so I guess you are testing some development copy somewhere else.
How do you use X-Payments in your checkout routine? As a separate page or via iFrame?
What do you see in X-Cart and X-Payments logs? See http://help.x-cart.com/index.php?title=X-Payments:FAQ#Where_can_I_find_X-Payments_logs.3F
about how to find those log files.