Hello,
Apple requiring a payment method such as a credit or debit card where you have enough account balance to pay for the item is not an uncommon observation.
Note the statements in:
Remove a payment method from your Apple ID - Apple Support
- If you have any active subscriptions, you must have at least one payment method on file other than Apple ID credit.
Sign in with your Apple ID - Apple Support - at the very bottom: "When you sign in to the App Store and other media services for the first time, you might need to add a credit card or other payment information."
Also:
How App Store and iTunes Store purchases are billed - How apps, content, and subscriptions from Apple are billed - Apple Support
- Some subscriptions might not be charged to your Apple ID balance.
And:
What you can buy with your Apple Gift Card or Apple Account balance - Apple Support
"Some purchases might require that you have a credit card on file, even if you use your Apple Account balance to make the purchase."
So the resolution will be to add a 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 --> Add a payment method to your Apple ID - Apple Support