Just tell the GA creator that you can't activate the game. If the key is a duplicate, he should provide you another one or else you are free to mark as Not Received (you can technically also do it now, but if you don't contact the GA creator you can get in trouble). If the key is region locked, he should ask for a reroll. In any case, there's not reason to have this mark against your account if the key was unusable. It's not too difficult to sort it out one way or the other, but you need to get back to the GA creator and tell him that whatever you agreed on previously doesn't work, because you ended up with an unactivated win.