Payment issue

Before you can add funds to your Apple ID, you must have a valid payment method on file. Learn about the payment methods that you can use with your Apple ID. Or learn how to create an Apple ID if you don't have one." See how to Add funds to your Apple ID https://support.apple.com/en-us/HT208687  Note that "after you authorize the payment, the funds ... [are credited] to your Apple ID. Then, you can use the credit to make purchases from the App Store or iTunes store. Need more help? Contact Apple support for help here: Get started

See If your payment method is declined in the App Store or iTunes Store https://support.apple.com/en-us/HT203005 I forgot to mention this possibility earlier.

As the message shows, contact iTunes Support. See the Apple Support articles below for contact information.   

iTunes Support – world wide 

Apple Support schedule phone call