Hey there! Good question!
I’d say that, if there is sufficient funds on the account and it’s still giving that error, this is a good article to follow:
If your payment method is declined in the App Store or iTunes Store:
https://support.apple.com/en-us/HT203905
If you can't remove your last payment method or use no payment method with your Apple ID:
https://support.apple.com/en-us/HT203905
The two may not be directly related, but I know that other factors may contribute to that error, such as an open subscription, a due balance, purchase sharing, etc.
Hope that helps! Otherwise calling Apple Care would be a good idea, perhaps they can provide more information as to the cause and a resolution if the article doesn’t help.
Best!