On minecraft pe, my invites won't pop up on my friends phone and vice versa

I want to play my friend on xbox but it usually says he's offline. His xbox gamertag is KingKri8701. When I invite him, it doesn't pop up on his iPhone and when he goes to the joinable friends it says none of your friends are online right now. Same vice versa, I can't get his invites or his name to pop up at all when he invites me