Callback function gives HTTP error 500

[silentbogo]

I'm using Opencart 3.0.2 w/ Materialize template 0.80.3 (OC3).
Currently having an issue with activating the callback feature. As soon as I add it to the main page, the whole website goes down with HTTP error 500. If I deactivate it in the admin panel again, then everything is back to normal.

[trydalcoholic]

Hello!
What version of php do you use? Do you have a clean OpenCart without any third-party modules? How do you try to add a module to the main page? The module is enough to just turn it enable.

[silentbogo]

Hello!
What version of php do you use? Do you have a clean OpenCart without any third-party modules? How do you try to add a module to the main page? The module is enough to just turn it enable.

I'm running PHP 5.6.30, clean OC install w/ materialize template and no other third-party modules.
There are few modifications to a couple of twig files and small customizations to a catalog filter module: nothing related to callback.
I've enabled the module, adjusted settings and that's pretty much it. As soon as I enable it, the whole site goes down. Had no time to debug it myself (too busy at work), but I'll try to check Apache logs this weekend.

[trydalcoholic]

Please send the data to access your site (ftp, admin panel) to my e-mail: gatalsky94@yandex.ru