1. Make sure you have a stable internet connection.
2. Check to see if your username and password are correct.
3. If you have the Facebook app installed on your device, log out of it (or delete and reinstall it).
4. Log out of your Facebook account in all browsers installed on your device (Chrome, Opera, Safari, etc.).
5. Restart your device and try to connect the game to Facebook again.

For Android devices:
1. Go to Settings -> Accounts.
2. Tap Facebook -> Remove.
3. Remove the game from the list of applications on Facebook.
4. Restart your device, enter the game, and try to reconnect it to Facebook.