Using apple gift card

I bought myself a £15 Apple gift card to use for Apple TV+.I redeemed the code and the £15 is in my Apple account but I am unable to use it for my intended purposes.Do you need to have a credit/debit card on file with Apple(received an answer from Apple) for this to work? ….And will the card be charged for the subscription instead of my Apple account with the £15 on it.