I don’t actually have a card

"Some purchases might require that you have a credit card on file, even if you use your Apple ID balance to make the purchase." - from: What you can buy with your Apple ID balance --> https://support.apple.com/HT211187

For a variety of reasons Apple will almost always require a functional payment method such as a credit or debit card be present when downloading anything from the iTunes or App Stores that isn't totally free, even if the item will be paid for with Apple Account balance. The only solution to satisfy this requirement is to add a valid payment method.

This document explains how to 'Change, add, [review,] or remove Apple ID payment methods' on a Mac or Apple mobile devices; click here --> https://support.apple.com/HT201266

'Payment methods that you can use with your Apple ID' --> hhttps://support.apple.com/HT202631

See if you can find somebody who is willing to trust you with their payment method. Additional options may be available if you are under 18 and you are using Family Sharing.

Approve what kids buy with Ask to Buy - https://support.apple.com/HT201089