How to set up family sharing using Apple gift cards as payment method only

I want to set up family sharing. I always fund my iTunes Store purchases with iTunes gift cards-never credit or debit cards. I’ve done this for over 10 years. I have money in my iTunes account but when I try to set up family sharing the system keeps asking me for another form of payment. I don’t like to leave my credit card number on websites. Not even Apple. Can I use family sharing with iTunes cards only?

Thanks