How can I verify and update my payment method on iPhone?

I am in Cairo, Egypt. Having said so, all my payments (local or US) for the first two days were working perfectly. Suddenly, Apple did not accept my credit card on file, which I have been using. I called the local bank issuer and was informed that they don't have any payment decline notification. I used the card on other shopping platforms and it's working! I can't update or purchase any of the apps.

[Re-Titled by Moderator]