Can I add my own payment method for the app store if i'm in a shared family?

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 ID 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

See ⤵️

What you can buy with your Apple Gift Card or Apple ID balance

What you can buy with your Apple Gift Card or Apple Account balance – Apple Support (UK)

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 ID balance and (2) then you need to set your Apple ID balance as your default payment.

(1) See -> Check your Apple ID balance

Check your Apple ID 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 update your payment method or add funds to your Apple ID balance, It would take about 1 to 3 business days in order to process.

If you're still unable to update your payment method, Contact Apple Support.

When you purchase something from the App Store or iTunes Store, the charges will be deducted from your Apple ID balance, before the organizer's credit card is charged.

See -> The gift card for everything Apple -> Apple Gift Card - Apple

This 'universal' gift card was launched in the US at the end of July 2020.

Since June 29, 2022, a number of European countries have been added, including Germany, France, Italy, Spain, the UK and the Netherlands.

(on macOS) Click Add money -> iTunes Store opens in iTunes.

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

• 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.

About Gift Card Scams -> About Gift Card Scams - Official Apple Support