iTunes card not working for purchases

Re: my iTunes card is not working if I want to purchase something

Here's how it works:

You can redeem your Gift card, so the money is available in your Apple Account for purchases from Apple:

See: How to redeem your Apple Gift Card, App Store Card or App Store & iTunes Gift Card

You can also: Check your gift card Balance:

and

See what you can buy:

Please Note:

Above linked article says: "Some purchases may require that you have a credit card on file, even if you use your Apple Account balance to make the purchase".