Coronavirus: Isn't it illegal for a merchant to refuse a cash payment?

I was in a store today and tried to pay by credit card. My card was declined. I said to the merchant, "I'll have to pay cash." The merchant said, "I'd prefer if you pay by card. Don't you have another card?" I said, "no." So he accepted my cash. But what if a merchant says, "I will not accept cash--only credit card." Isn't it illegal for a merchant to refuse cash? If you look at money it says, "This note is legal tender for all debts, public and private."