GetFriendsList (server) returns null list for other player

When we try and get the player list from another player through cloudscript, it always returns 0 in the list.

However, it works if we use our own playfabID? Why would this be happening?

Have even tested manually entering a platfabID on our cloudscript:

    var getPlayerFriendsRequest = { "PlayFabId": "xyzplayfabID" };
    var friendData = server.GetFriendsList(getPlayerFriendsRequest);
    var message = friendData;