Gift card purchases
Do you have to have a debit card listed as a payment option for it to use gift card money for in app purchases?
Question marked as
No, you don't need to have a debit card listed as a payment method.
Read again -> Related Article -> How to redeem your Apple Gift Card or App Store & iTunes gift card
When redeeming a gift card, the amount will be credited to your (1) Apple ID balance and (2) 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)
Change, add or remove Apple ID payment methods
Change, add or remove Apple ID payment methods – 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.