I try to change my payment information but iphone said “cannot update payment information” what should I do?
iPhone 8 Plus, iOS 13
Log into your account in the App Store/iTunes and you should be able to change/verify it there. Or you can click the blue Edit payment methods in the article below. When signed in and the page loads, you will be on the credit card page. After updating that, click the Go Back button at the lower left and you will be on the address page.
Was there a link for you to use? if yes, then use it. If no, see If your payment method is declined in the App Store or iTunes Store https://support.apple.com/en-us/HT203005
i have the same issue as well .. saying "Your request to buy using mobile phone ...... was declined because there may be a billing issue with your mobile account. Go to the iTunes Store on your computer and update your Billing info.
As the message shows, contact iTunes Support. See the Apple Support article below for contact information.
Payment information
