Cannot Add Apple Credit Card to My Payment Methods using iPhone

A Family Sharing member tried to make a purchase and got a message that the payment method can't be used with the iTunes store. I'm the organizer, and the payment method I had on file was my Apple credit card. I added a different credit card, deleted my Apple card, and unsuccessfully tried to add it back again via "Add Payment Method." I tried doing so two different ways:

• Clicked on Apple Card "Found in Wallet". Selected "Done" and "Double Click to Add". Appeared to "Process the Payment" but doesn't show up under my Payment Methods.

• Clicked on "Credit/Debit Card" and entered my Apple Card number, expiration date, and CVV. Got the message: "This payment method can't be used with the iTunes Store.

I'm very confused as my Apple Card was previously used for iTunes purchases without any issues. Any suggestions?