Can't update payment credit card what can I do?

Follow the steps here: link-> Change, add, or remove Apple ID payment methods - Apple Support

Thank you for your link - which clearly states "If you use Family Sharing and Purchase Sharing is turned on, the family organizer must update their billing information or add a new payment method." WRONG - the family organiser CANNOT add a new payment method - at least not on our accounts. Both account and ipad remotely checked out by a senior Apple technician yesterday afternoon (after it was escalated by an online customer support agent) and concluded unsolved and that even he was unable to provide an answer as to why an additional payment method can no longer be added to the shared account (despite the fact that Apple is accepting, and confirming, a direct debit agreement via Paypal, but then not adding that information to the account.

The Family Organizer must have a payment method at all times.

If the current payment method is not being accepted, you need to add another one before you can remove the one that is to working.

Any purchases started by the family organizer will use their payment methods.

Other Family Members ion thew family group will use the Family Organizer's payment methods.

If the iPad is logged in with a different Apple ID than that of the Family Organizer, then it will not use the payment methods added to the member's account. It will only use the Family Organizer's payment methods, but they need to be verified.

If they cannot be verified, contact the credit card issuer or bank for the payment method in question.

Why not? What happens when you try? Do you get an error? If so what does it say?

Link-> If your payment method is declined in the App Store or iTunes Store - Apple Support

additional payment method will not update on the account

...plus, the family organiser is still unable to access any payment method on the ipad. Just tries to connect to the information but fails (even after 30 minutes of waiting).