Trying to pay for Apple subscription after redeeming iTunes gift card but it won’t even try to use it as an option. How can I pay for my Apple Music subscription with my Apple ID balance?

>>Apple Gift Card and Apple Account

balance can't be used for some purchases

• You can't use your Apple Account balance to send gifts or gift cards.
• For some recurring charges, like AppleCare+, you can't start your subscription with Apple Account balance. But as long as you keep another valid payment method on file and your Apple Account balance would cover an entire charge, your recurring charge will pull from your Apple Account balance.*
• Some subscriptions might not be charged to your Apple Account balance.
• If you use Family Sharing, your family members can't spend your Apple Account balance. Funds that you add to your Apple Account balance are available only to you. Learn more about how purchases bill to your Apple Account balance.<<

What you can buy with your Apple Gift Card or Apple Account balance - Apple Support