Trying to buy more storage for my iCloud subscription

it says payment declined and shows failed where my card was added.

See -> If your payment method is declined in the App Store or iTunes Store

If your payment method is declined in the App Store or iTunes Store - Apple Support

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Get more help

• If you disputed a charge from the App Store or iTunes Store, contact your financial institution again to authorize that charge and future purchases from the App Store or iTunes Store.
• If you're outside of the United States, you might need to contact your financial institution to allow international purchases.
• In some countries and regions, your payment method might be declined because of changes to local law. Learn about billing and purchases in Europe or what to do if your card is declined in India.
• If you still need help, contact Apple Support.

Click here for more support and assistance.