Hey rAw32,
If I understand correctly, you have an existing balance on your Apple ID and you want to be charged there and not use a different payment method. This shows that you will be billed using an existing balance first.
"This is the order in which Apple attempts to charge your payment methods:
- If you have an Apple ID balance, Apple attempts to use your Apple ID balance to cover the full amount of the bill.
- If you don't have an Apple ID balance or you don't have enough balance to cover the full amount of the bill, Apple attempts to charge your primary payment method. Your primary payment method is the payment method that's listed at the top of your Manage Payments page."
How App Store and iTunes Store purchases are billed
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