How can I buy in-app gems using Apple account funds?
How to purchase in app gems with Apple account money
[Re-Titled by Moderator]
Question marked as
If the app supports and allows it yes.
Apple Account funds will be used automatically before any other payment method when making any purchase including in-app purchases. You don't have to do anything.
If there is an issue with an existing payment method, you will need to resolve that before it'll use the Apple Account funds. Once the issue is resolved it will use those fund first before charging the other payment method.