Issues with RCM V3 adapter

I’ve been trying to pair my wii guitar but I keep getting to the “you need a controller for this game” screen. I am having my controller plugged in to the adapter, holding the + and plugging in the adapter and when I am in the menus of xbox, I can move but in fortnite I can’t, even when I begin a game. And when I try plugging the adapter in while in fortnite I get the “you need a controller for this game.” What am I doing wrong?