Apple Gift Card

I am not clear what you are asking. When you redeem a card the value is added to your Apple Account balance. It is then automatically used to pay for items.

How App Store and iTunes Store purchases are billed. Click here --> https://support.apple.com/HT201359

"Which payment method is charged?

When you buy items or pay for subscriptions, Apple automatically attempts to charge your payment methods in this order:

1. Apple attempts to use your Apple ID balance to cover the full amount.

2. If you don't have Apple ID balance, you don't have enough to cover the full amount, or an item cannot be paid for with Apple ID balance, Apple attempts to charge your primary payment method (typically a credit or debit card, but varies according to country). The primary payment method is at the top of the list in Settings on your iPhone. You can control which payment method is at the top of the list.

3. If there's a problem with the primary payment method, or if the primary payment method can't be charged for the full remaining amount, Apple attempts to charge your other payment methods in order from top to bottom. If none of them can be charged, Apple may try again.

Create or use your Apple ID without a payment method - https://support.apple.com/HT204034

- "You can remove payment methods from your existing Apple ID after you sign in to the App Store, iTunes Store, or Apple Books. You won't be asked for a payment method again until you make a purchase." One interpretation of this is if you want to "get" anything you must have a accepted payment form (e.g., card) on record. BUT: I download only free items and have never had to enter a card so I read this as instead meaning if you get something you truly "purchase" and actually costs money.