Make sure you have allowed the use of Facebook to sign in to third-party sites and applications ( Settings-> Apps and Websites-> tap on the Edit button in the Apps, Websites and Games section-> check if the setting is turned on).Open Facebook Settings (using the mobile app or website version).Restart your device and try to connect the game to Facebook again.Log out of your Facebook account in all browsers installed on your device (Chrome, Opera, Safari, etc.).If you have the Facebook app installed on your device, log out of it (or delete and reinstall it).
Check to see if your username and password are correct.Make sure you have a stable internet connection.
