[Amads]

Code:

SendClientMessageEx(targetid, COLOR_AQUA, "%s has invited you to join the %s", ReturnName(playerid), ReturnFactionName(playerid));
SendClientMessageEx(playerid, COLOR_AQUA, "You have invited %s to %s", ReturnName(id), ReturnFactionName(playerid));

You had the wrong player's ID.