If you can’t download or update apps on your iPhone or iPad - https://support.apple.com/HT207165
- "You might need to have a payment method on file, even if the app that you want to download is free." If you have something else on your account that requires a payment method, such as a subscription, and your current payment method is not working then Apple won't let you download even free things until you fix the payment method. This is explained in this document, 'If your payment method is declined in the App Store or iTunes Store' - https://support.apple.com/HT203005
Get your Family Sharing Organizer to review the payment methods used and to make sure there is at least one that works.
This document explains how to 'Change, add, [review,] or remove Apple ID payment methods' on an Apple mobile device, a Mac, or a PC; click here --> https://support.apple.com/HT201266