Go here! If you are having trouble redeeming the code it may have reached its maximum uses. If so, a popup will say "Sorry. This redeem code has passed its maximum uses.” You'll need to keep on the lookout for a code again; to get more, watch Streams live or look for developers in Global Chat.
Invite code invalid
Unfortunately, due to legal issues and restrictions with various platforms, only PC, iOS, and Android users are able to redeem codes. Console devices are not able to redeem codes.