Updating billing info on itunes
Please enter valid payment method information.’ I contacted Apple i Tunes Support on their Support page, Here is what answered I received from them.
Monthly charges are billed at the beginning of your billing cycle and may take a few days after the billing date to appear on your account.You can of course change your credit card information from i Tunes itself, but you are also able to update your payment information from an i Pad, as explained in this tutorial." error message; all you need to do is tap on "Done", start over from the top of this tutorial, and then edit your payment information as soon as the screen opens.(Only if i Tunes & App Store Gift Cards are available in your country.) Welcome to i Tunes Store Customer Support.I’m sorry to know that you have been getting error message as “Your credit card was declined” when you are trying to update your debit card.
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It solved the problem within minutes however, it may not work for everyone.