Zalc: "Make sure the "family payment method" is a Citi or BofA virtual number with a $1 spending limit and a expiration set for 12 months (the maximum).
Otherwise all members can spend on the card on Apps without authorization.
Write down the CVV of the virtual number, as you need it to add new members to the group.
You do NOT need to use the virtual card to pay the $15/month, you can use any cards in your Google wallet."