Why I can’t update my payment

See if any of the following articles can help:

• Payment methods you can use with your Apple ID - Apple Support
• Change, add, or remove your Apple ID payment methods - Apple Support
• If your payment method is declined in the App Store or iTunes Store - Apple Support

You will then need to contact your financial institution for the payment method that you are trying to use. Apple does not control this. They either accept or reject the payment method based on its validity.

Did u see the info in the articles Tesserax gave?

”If you have trouble adding a payment method for purchases in the App Store, iTunes Store or Apple Books, you might need to contact your financial institution for more help.”