Create new group, but Player ped can't be member

Hi, I want to create a group and set the player as a member of this group. But it doesn’t work. The player’s group still the same. The new group is correctly created. I spawned some ped belonging to this group and everything is fine. It’s also fine when I spawn some peds and set them to the default group of the player. But the invert seems to not working.
Any idea why?

            int GroupID = Function.Call<int>(Hash.CREATE_GROUP, 12);
            Function.Call(Hash.SET_PED_AS_GROUP_MEMBER, Game.Player.Character, GroupID);
            int MyGroupID = Function.Call<int>(Hash.GET_PLAYER_GROUP, Game.Player.Character.Handle);
            Screen.ShowNotification("New group number: " + GroupID);
            Screen.ShowNotification("Player's group number: " + MyGroupID);