iTunes
Q: how do I change my payment method -cannot change the family sharing card
despite changing my new card information - payment method is not being updated.
iPhone 6 Plus
Posted on Jul 18, 2016 9:41 PM
by King_Penguin,Apple recommended
iTunes
You are logging into the family organiser's account and changing the card on that account : Change or remove your Apple ID payment information - Apple Support
Only the card on the organiser's account can be used, any card on members accounts won't be
Posted on Jul 18, 2016 11:29 PM