game wont accept itune card credits
My son has a game on his I pad air and he wants to buy some gems to upgrade his game play, but when prompted for payment it says "this item is for an app that was purchased by a different Apple ID. To buy this item with this Apple Id, you must first purchase the app". Clash of Clan is a free game, i don't understand why he needs to purchase it. We bought him and loaded itune cards on his IPad and he has credits for his purchases but cannot do it.
He's been playing this game for a while now and doesn't want to lose his progress.
Thanks in advance.