I cannot update payment method on App Store

Re: "New payment card: Why can I not update my new payment card? "

We can not guess the cause of your situation, as we know so little about your difficulty.

Eg: Are you getting an error message that may point to the solution ?

You may want to check that your iOS software is updated to the newest compatible version:

Eg: Check Settings > General > software Updates ... to see if an update is waiting to be installed.

(Updates often provide important security updates and are then recommended for all users.)

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Else, if the iOS already updated:

You could try restarting your iPhone (deletes temporary files, updates recent setting changes, and often restores order if something is not working): How to: Restart your iPhone - Apple Support

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You can also check you are signed in (to your iPhone) with the correct Apple ID:

Sign in with your Apple ID - Apple Support

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See if following the steps in Apple support's online articles can help: (NB: If you have active subscriptions: you may need to add a new method before deleting an old one)

How to: Add a payment method to your Apple ID - Apple Support

Remove a payment method from your Apple ID - Apple Support

or

If you need to change or update your Apple ID payment method - Apple Support

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Trouble-shooting if needed:

You may want to check the payment method is one that Apple can accept in your country:

See: Payment methods that you can use with your Apple ID - Apple Support

or

If a message says 'billing problem with previous purchase' or 'verification required' - Apple Support

All the best :-)