Problem making shortcut with function keys

I have installed an new screenshot app and want to make a shortcut for it. To make a screenshot of the current monitor I want to add Alt+Print. On my keyboard I need to use a Fn key to use the Print screen key. When I do this in the settings menu Alt+SysReq is added instead of Alt+Print. How can I change this?

You don’t have to use the Print screen key. For example, I use Super+Ctrl+A to take a screenshot of the active window.

I have now used the shortcut Alt+Ins. But it is strange that you can’t use the Print key as a shortcut key.