In order to get players in this list you need to invite a person that is new to the game, who has never played it before.

Even if they have played the game for 2 minutes; those players will not be taken into account as the game will have been considered as installed.

Also, you need to be the first person who invited this player, and they need to join via the exact link you send via the Goliath invite page

To finish with, in order to validate those players they will need to reach level 5 once you have added them.

Spending 200 Golds will enable you to bypass inviting a friend.