How to sign into game center if you don't have an email as your apple ID
I registered this game center account a couple of years back, and at that time you didn't have to use an email as its apple id, so it was basically just a nickname and the password. A couple of months before I could still log in, but when I tried to sign on to a new device a week earlier, game center said that it was an invalid Apple ID. I tried to see if it was my iPad's problem by signing out and then trying to sign back in with my phone, but that also didn't work. Both my phone and my ipad are iOS 10, and it still didn't work when I tried on my iPod, which was iOS 8.4. Did Apple cancel the function? And how can you get the data from apps that use rely ONLY on game center (say, clash of clans and clash royale) to transfer if you can't log in to your game center?
iPhone 6s, iOS 10.2