I no longer have credit card that's registered on iTunes, when try to delete it, it says, unable to remove
"family organizer requires at least one payment on file." how can I edit and/or add another credit card?
iPhone 6 Plus, iOS 12
See this support article-->Change, add, or remove Apple ID payment methods - Apple Support. You can add another card, then make the new card the default. You can then delete the old card.
Assuming you are the Family Organizer:
Change, add, or remove Apple ID payment methods - Apple Support
CREDIT CARD IN ITUNES
