Internal Server Error during finishing checkout

Hi, i’ve got an issue with the plugin during the checkout.
It doesn’t allow me to redirect the page into the “order success page” but stays in checkout page. with a notice “Internal Server Error”. However the order is placed, and new order email is sent. Please check printscreen.
So the issue is it doesn’t redirect user to the success page.

note: there must be a conflict with other plugins/payment method, because when i disable this plugin, the redirection works just fine.