There might be 2 reasons for that:
- You've reached the 100 friends limit. At present, there is no option to remove friends from your friends list.
- You've restricted the app's access to your friends list on Facebook.
To allow the app to access your friends list, please follow the steps below:
- Go to the Crew screen in the game.
- Tap the button "Continue with Facebook" in the "Invite friends" section.
- Log in to your Facebook account if necessary.
- Allow the app to access your friends list.