Hi lucyrockville,
I understand that you are in a family for Family Sharing, and you've added iTunes Store credit, but you're being asked to verify the billing information for your account. I'm happy to provide some help for this issue.
If you are the family organizer, you still need to make sure there is a valid payment method for the family to use. You can use the following article to learn how to verify your billing information, and change it if necessary:
I understand that you are in a family for Family Sharing, and you've added iTunes Store credit, but you're being asked to verify the billing information for your account. I'm happy to provide some help for this issue.
If you are the family organizer, you still need to make sure there is a valid payment method for the family to use. You can use the following article to learn how to verify your billing information, and change it if necessary:
Change or remove your Apple ID payment information - Apple Support
Additionally you can learn more about how Family Sharing purchases and payments work below:
Family purchases and payments - Apple Support
Thanks for using the Apple Support Communities. Cheers!