How to add a credit card to my Apple ID when on a Family Sharing account

You cannot. There is nothing that needs fixing because this is very intentional and makes Family Sharing possible.

Only one person, the Organizer, can (and must) have a card, but the Organizer can avoid having this charged by others by asking them to make sure they have adequate personal balance (e.g., from gift cards) to cover their purchases. Other family members can only pay for things by using their personal balance or by letting the remainder automatically roll over to the Organizer's payment method (such as a credit card but not the Organizer's personal account balance).

The alternative is described in this document: Add a family member to your shared subscriptions - Apple Support

"If you're the family organizer and you don't want to pay for family members' purchases and subscriptions, you can turn off Purchase Sharing [ How to share apps and purchases with your family - Apple Support ]. When Purchase Sharing is turned off, everyone must use their own payment method. When Purchase Sharing is turned off, family members can share subscriptions, but they can't share individual purchases like apps or books."

Another alternative would be for a person to leave the family group altogether. However, a person can only join one family per year.

=Full details=

Based on: How to share apps and purchases with your family - Apple Support and How apps, content, and subscriptions from Apple are billed - Apple Support

1. If anybody in the family buys or subscribes to something, Apple first attempts to charge the item to that individual's Apple Account (Apple ID) balance, if any.

2. If a family member does not have enough personal Apple Account balance, any excess will be charged to the Family Organizer's primary payment method (usually a card of some kind). The Organizer's personal balance will not be used for purchases made by other family members. If Apple cannot bill the primary payment method, the Organizer will need to make another payment method the primary method. With Family Sharing the Organizer always has to have at least one functioning payment method.

Also note: "Some purchases, including gifts, can't be billed to Apple ID balance and will be charged to the family organizer's payment method." "Some subscriptions might not be charged to Apple ID balance."

Ref:

- Family purchases and payments - How to share apps and purchases with your family - Apple Support

- How apps, content, and subscriptions from Apple are billed - How apps, content, and subscriptions from Apple are billed - Apple Support

- Check your Apple ID balance - Check your Apple Account balance - Apple Support

- Add a payment method to your Apple ID - Add a payment method to your Apple ID - Apple Support

Adding funds to your Apple ID balance:

- How to redeem your Apple Gift Card or App Store & iTunes gift card - Apple Support

- Add money to your Apple Account balance - Apple Support

You can add a second credit card to an account, but it has to be done through the Organizers end of things. My wife and I share a card so I can add hers by adding my copy of it. If you don't want to pay for another person's things then make sure they have personal balance on their account so that gets charged first.

You may wish to reason it out. First, remember (as it says in the fine print below) that the people here are just other Apple products users like yourself. I understand people, I understand what you want, but I also understand what Apple has devised and that's what we do on this forum. It is a very clever way to ensure that Family Sharing remains between a trusted group of people and not somebody a person met on a chat group yesterday and decided to try to share a lot of music with. We may not like it but unless you can think of a better way of ensuring sharing remains between a tight knit group of people, its what Apple has come up with. Also remember that Apple is likely not the only one in this. Apple just sells media and things written by other people and their distributors. If the distributors aren't happy with the solution then they won't let Apple sell it.

If you wish for Apple to hear your displeasure then read Product Feedback - Apple

People have been complaining about this for years. One thing they don't remember is that it used to be that no sharing was possible at all. Everybody had to buy their own copy of everything. So in that regard what Apple did was go to bat for you and make sharing possible, just as it might have been 30 years ago when the family had a LP collection. In fact this is even better than then because now a family member can be anywhere in the country, not just you walking down to your sister's door and telling her you want your copy of the BeeGees back.

Hello,

You can’t do it, if you want to pay by your card your Wife need to disable Family Sharing.

Have a nice day ☆

Mateusz

That's what I have been telling you all along (except I think it is very, very clever design and I challenge you to find something that works as well). I know you don't like the system but it serves its function. You can bet there's plenty of people who want to abuse the Family Sharing system and your method would let them do just that. Then likely the whole policy would cease and we'd be back to having everybody paying for their own copy again. You're kind of shooting the messenger though.