The easiest solution would be using Apple Account balance, which can also be used to pay for most In-App purchases. You can top up your Apple Account balance by redeeming Apple Gift Cards, if available in your region, or by transferring money from your banking account.
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- In countries and regions where Apple Gift Card is available, you can use your Apple Gift Card or Apple Account balance to buy products and accessories at apple.com, an Apple Store, or in the Apple Store app. In these countries and regions, your Apple Account balance includes the balance from any Apple Gift Cards or App Store & iTunes Gift Cards that you have redeemed.
- Buy apps, games, or in-app purchases from the App Store.
- Buy music, movies, and more from the iTunes Store, Apple TV app, or Apple Books.
- Pay for subscriptions like Apple Music, Apple Arcade, and Apple TV. Or pay for subscriptions to apps from the App Store.
- Pay for iCloud+, Apple's premium cloud subscription.
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- 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.
copied from: What you can buy with your Apple Gift Card or Apple Account balance - Apple Support
Add money to your Apple Account balance - Apple Support
