How do you add an Apple gift card
How do you download an Apple gift card to pay for iCloud
iPhone 7 Plus, iOS 15
Question marked as
You redeem gift cards onto your Apple ID, and then their credit balance is automatically used when you make purchases or subscriptions are billed.
click here ➜ How to redeem your Apple Gift Card or App Store & iTunes gift card - Apple Support
This does not preclude the need to have a valid payment method on file, or verify an existing one if a payment was unable to be made to it. It just causes the actual payment method to come out of the gift card balance first.