What u mean by that? Do you mean the itunes balance credits can not be used to pay in-app purchses? I have enough credits in my app store account but I cannot buy any in-app purchase. It shows that your purchase could not be completed.
I think that it needs a credit card attached to the acount of the gift card credit... I don't have a credit card that match the "nationality" of that store **** it! I paid more than 50$ and I can't use them in in apps???