Why can’t I subscribe with my iTunes card?
I want to subscribe for an app with my iTunes card
iPhone 6s, iOS 15
Why not?
What happens when you try?
You should just need to redeem the gift card onto your account. Any subscriptions you start will then use the balance of the iTunes gift card automatically.
click here ➜ How to redeem your Apple Gift Card or App Store & iTunes gift card - Apple Support