I can’t use my debit card on App Store. Why is that?

See -> Payment methods you can use with your Apple ID

Payment methods you can use with your Apple ID – Apple Support (UK)

fyi: Not all credit & debit cards seem to work with App Store / iTunes Store, try a different one, or preferably a credit card. If your card is not accepted as a paymenf method, you need to contact your bank.

Is your debit card issued by a bank for use with an account in the bank? Are there funds in the account?

Is your card a prepaid debit card that you bought from a store? Apple often does not accept this type of debit card.

M1 Mac mini, macOS 13.4;  Watch, series 7 GPS/cellular, watchOS 9.5.2; iPad Pro 2nd Gen, iPadOS 16.5; iPhone 12 Pro, iOS 16.5; TV 4th Gen, tvOS 16.5; HomePods, audioOS 16.5 and Airport Express w/ Airplay 2