Q: change family sharing payment

I just had to look up how items are billed...basically on Family Sharing the Organizer (your husband) gets charged on credit card for any purchases made by anyone else in the plan. So even (which is my problem now) if he had Apple store credit to cover your purchase it wouldn't use the store credit. It would charge the card. If you want to pay for your own downloads you have to have your own apple balance to pay for them.

Family purchases and payments - Apple Support

It states: After you set up your family, any time a family member initiates a new purchase it will be billed directly to your account unless that family member has gift or store credit. First, their store credit will be used to pay the partial or total bill. The remainder will bill to the family organizer's card. As the family organizer, any receipts generated by the transaction will be sent to you.

if you follow the other link: How iTunes Store purchases are billed - Apple Support

When you initiate a new purchase, it will be billed directly to the family organizer's account, unless you have gift or store credit. First, your store credit will be used to pay the partial or total bill. The remainder will bill to the family organizer. iTunes Store credit on your account isn't shared with other family members. So if the family organizer has a $50 credit on their account and another family member initiates a purchase, it won't deduct from the organizer's iTunes Store credit, but will bill the organizer's credit or debit card.

I am annoyed at this. There should be an option to allow to use 1) your own credit card if you are an adult and 2) as the Organizer, authorize to use apple credit.