I can’t take you to civil court if I’m claiming you won't pay for something as you stand there waving the money in front of my face.
On this front. If you owe them money, they must accept cash. This is why people can pay thousands of pennies at tow yards. Or if you eat at a restaurant and they bring the bill, they can't then say they'll only take card, they must accept the cash.
Physical money is "...legal tender for all debts, public charges, taxes, and dues." Notice that purchases/private charges or trades are not included in that.