How to use Apple ID for payment method

See the Apple articles below:

How to redeem your Apple Gift Card or App Store & iTunes gift card

How to redeem your Apple Gift Card or App Store & iTunes gift card – Apple Support (UK)

When redeeming a gift card, (1) the amount will be credited to your Apple Account balance and (2) then you need to set your Apple Account balance as your default payment.

(1) See -> Check your Apple Account balance

Check your Apple Account balance – Apple Support (UK)

(2) See -> Add a payment method to your Apple ID

Add a payment method to your Apple ID – Apple Support (UK)

If you already use your Apple Account balance, the Apple Gift Card or App Store & iTunes gift card is automatically added to your Apple Account balance.

If you update your payment method or add funds to your Apple Account balance, It would take about 1 to 3 business days in order to process.

If you're still unable to update your payment method, Contact Apple Support.

If you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK) 

If you're using an iPhone with Apple Wallet, here's a link to show you how:

Add your Apple Account Card to Wallet on iPhone - Apple Support

If you're using a Mac (latest software)

System Preferences

Your Name at the top

Media and Purchases

Next to "Account", select "Manage"

Scroll down to "Apple Account" and click "Add Money"

If you have a balance on your card, by default, this money will be used for App Store purchases.