can't login check info

My brother has been trying to play for a couple days and when he clicks into the game it gives a message that says "can't login check your information." He can login in the app no problem and his account won't even work on my Xbox. All the info we can find on this problem is for PC and we've tried just about everything related to Xbox restart or wifi restart, but to no avail. If anyone has any ideas please let me know!