Numpad does not react in games?

I use my Numpad eg. To mute my microphone while I'm on the TS. If I browse the internet in the normal way, it will work fine. However, when I'm in Fortnite and want to mute my microphone, that's not reacting anymore…

Does anyone have an idea here?

Did you really set Numpad as the key assignment? If so, then I have no idea. Otherwise, the numpad will always work

I have the Numpad and use it just to my microphone and my speakers to mute and that works perfectly on the normal desktop. But when I'm in the game, not anymore…