Need to fix the bug in php on the OpenCart engine

Hello!
There is a small shop on OpenCart it is very poorly made, both backend and front.
Im doing refinements on the front on it, Im not really in the back so I need to help fix the bug.

The error is that the payment page has a white screen and errors in html in the browser.

I havent done anything already, and the modifiers have removed everything and the modules in turn, and the bugs have been corrected in PHP and that nothing helps at all. So you have to be no new to PHP and opencard.

You need to correct the situation as quickly as possible, in response write your telegram necessarily and for how long you solve the problem.