How can I make my Apple Gift Card pays instead of bank card when purchasing?

Not all purchases can be made with Apple Account balance:

...

• 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 be pulled 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.

* In some countries and regions, your Apple Account balance can’t be used for some subscriptions like AppleCare+. Check if Apple Account balance in your country or region isn’t supported.

...

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