There are a few reasons as to why this may be happening:
1. Your friends aren’t logged into Facebook
2. The connection between THE GAME OF LIFE and Facebook has expired or become corrupted
3. The Facebook plugin is experiencing technical difficulties
To reset and force a new connection between the game and Facebook, please make sure that all players do the following:
1. Log into Facebook on the web browser on your devices
2. While on Facebook, go to Settings – Apps, and clear THE GAME OF LIFE from the list;
3. Open THE GAME OF LIFE again and a message should appear saying your Facebook connection has expired and asking all of you to login again
After this, you should be able to invite your friends normally. Make sure that they have the game open and are either on the Main Menu or on the World Selection screen.
Should the issue persist despite the above troubleshooting steps, try having one of your friends do the invites instead!