Hi @serhatvilla7 and thanks for reporting this.
It looks like your account is already linked to both iOS and Android so you cannot link it to a second GameCenter account.
@QuimSWGoH Thank you very much for the long answer. You must have spent so much time to answer my question, I really appreciate it. I will try what you suggest.
@serhatvilla7 I can confirm that the method that I explained works, because I got link an account to Game Center when already was linked to Google Play and Game Center at same time, so now is linked to 3 sites at same time. The only problem was that if you have the new mail connected to Game Center before link the account to the guest account and, by error, you connect to the game, also if you almost not started the tutorial, if you only saw the "Have an account?" button but you forced to close the game just after it, it seems the account cannot be linked and is wasted, so to link it is needed, first of all, link the account (connecting to Facebook in the Google Play account) to the iOS guest account, being sure that in the Game Center settings there is not any account connected. Once is linked then you can connected your new Apple ID and it should ask if you want continue the game or start a new game, you press in continue game and automatically is linked. So is important there be sure your new Apple ID is not connected to Game Center before link the account to the guest account or your mail will be wasted and will be needed create a new one. See you!!
