I cant play co op rivals with nmy freinds team

I have no clue how to fix this and im hoping someone has a solution. me and my mate were able to play co op a couple days ago with mine and his team (hes on xbox im on pc) and now if he tries to invite me to play with his team it doesnt show me on his freinds list and he cant invite me but i can invite him to play with mine and when im offline i show up on his freinds list to play. Has anyone had this problem and found a fix for it?