Recently, Facebook updated their permissions requirements for all apps. To ensure the game app has access to log you in with Facebook, please follow the steps below.

1. Open the Facebook App
2. Tap the Menu Hamburger (3 lines)
3. Tap "Account Settings"
4. Tap "Apps"
5. Tap "Logged in with Facebook"
6. Select the "Expired" tab
7. Select the app in the list of apps
8. Tap the blue "Renew Access" button