If you are a member of family sharing, the only payment method that can be on file is the organizer's card.
You can have your own payment method with your Apple Account balance.
See -> Make sure that each family member has a unique Apple ID
Make sure that each family member has a unique Apple ID - Apple Support
When you purchase something from the App Store or iTunes Store, the charges will be deducted from your Apple Account balance, before the organizer's credit card is charged.
See the Apple articles below:
What you can buy with your Apple Gift Card or Apple Account balance
What you can buy with your Apple Gift Card or Apple Account balance – Apple Support (UK)
- You can't use your Apple Account balance to send gifts or gift cards.
- Some purchases might require you to have a credit card on file, even if you use your Apple Account balance to make the purchase.
How to redeem your Apple Gift Card or App Store & iTunes gift card
How to redeem your Apple Gift Card or App Store & iTunes gift card – Apple Support (UK)
When redeeming a gift card, (1) the amount will be credited to your Apple Account balance and (2) then you need to set your Apple Account balance as your default payment.
(1) See -> Check your Apple Account balance -> Check your Apple Account balance – Apple Support (UK)
(2) See -> Add a payment method to your Apple ID > Add a payment method to your Apple ID – Apple Support (UK)
If you already use your Apple Account balance, the Apple Gift Card or App Store & iTunes gift card is automatically added to your Apple Account balance.
Where to buy a physical Apple gift card:
Actually, you can buy an Apple gift card at many places, it depends of course on where you live.
At an Apple Store or an Apple Authorized Reseller in your region certainly, but also at a good bookstore, supermarket and/or drugstore.
Also read the articles below ⤵️
If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card
If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support
check ⤵️
Card is not valid
Card has already been redeemed
Card is not activated
Code is unreadable
Code must be redeemed in a different country or region
- You can't redeem Apple Gift Cards or App Store & iTunes Gift Cards outside the country or region of purchase. For example, if you bought an App Store & iTunes Gift Card in France, you can't redeem it in the App Store in the United States.
Contact Apple Support -> Contact Apple Support.
About Gift Card Scams -> About Gift Card Scams - Official Apple Support
If you have followed all the steps and instructions and if you still need help, get support from Apple directly -> Get Support or call Apple in your region see -> Contact Apple for support and service or check -> here for more support and assistance.