Unable to add credit card as a payment method to Apple Account

Does it say why not? If you can't tell us anything more then we have to guess as to the reason. Generally my first choice is your iPhone was swallowed by an alligator. In the meantime, enjoy reading this long list of possibilities:

This document explains how to add a payment method to your Apple Account on a Mac, Apple mobile devices, PC, or online ➔ Add a payment method to your Apple Account - Apple Support

On an iPhone or iPad (note that the details may vary slightly depending upon which iOS version you are running) :

1. Open the Settings app.

2. Tap your name.

3. Tap Media & Purchases (or Payment & Shipping). You might be asked to sign in with your Apple ID.

4. Tap Manage Payments. Depending upon the iOS version you use you might not see this step.

5. Tap Add Payment Method. Enter the new payment method, then tap Done.

If an app or feature on your device is not working, not appearing, or is restricted (grayed out), a frequent reason is it may have been disabled using Screen Time, or by an IT administrator if you are using a device owned by an employer or educational institution.

- Read this support article If your Apple ID or other options are greyed out in Settings —> If your Apple Account is grayed out in Settings - Apple Support

Tap Settings > Screen Time > Content & Privacy > scroll to Allow Changes and turn on.

- If the device is managed (Settings > General > VPN & Device Management), contact the IT department that is doing the managing.

If you can't add a payment method, check Add a payment method to your Apple Account - Apple Support , or this one about what to do 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

- Apple is checking with your financial institution if the payment method is valid and receiving a negative, or no, response. Make sure the name and address are entered exactly as it appears on your financial institution bills and that the 3 digit CVV is correct. Check with your financial institution about the status of your card. “If you want to know why a debit card, credit card, or other payment method was declined, speak with your financial institution. Apple doesn't have information about why the payment method was declined.”

- Make sure your payment method is up to date or to try a different one ( If you need to change or update your Apple Account payment method - Apple Support ).

- Make sure this is one of the payment methods that you can use with your account, as listed in this support article: Payment methods that you can use with your Apple Account - Apple Support .

・Unfortunately the payment methods list is somewhat general and does not include individual brands of cards (I guess there are too many and are constantly changing). This thread is an example of where a person was not using an acceptable kind —> Why are my cards not supported on the MFI… - Apple Community

・Also read any footnotes in the document.

・If you are trying to use a payment method from another country you may encounter problems. Apple’s statements to me are unclear. In If your payment method is declined in the App Store or iTunes Store - Apple Support Apple implies international payment types can be used when it says, "You might need to ask your financial institution to allow international purchases on your debit or credit card". Apple then counters this in Add a payment method to your Apple Account - Apple Support with, “If you're using an accepted payment method but your Apple Account is set to a different country or region, change your country or region.” Usually it is easiest to just use a card from the same country as your Apple Account setting.

・Finally, note that the document only says which methods _are_ acceptable. Apparently certain types (usually a credit or debit card) _must_ also be present under certain situations such as when a subscription is involved.

If you still have problems, contact official Apple Support. Click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

See a list of Apple phone numbers around the world, in this article --> Contact Apple for support and service - Apple Support

If you're in India, click on this link to read an April 2022 notice 'About billing for Apple subscriptions and media products in India' --> About billing for Apple subscriptions and media products in India - Apple Support

Additional verification that may be required when making purchases in Europe --> https://support.apple.com/108103