IIRC, in North America the merchant must accept any form of legal tender when it is for purposes of paying off a debt (e.g. I'm at a restaurant and I've eaten the food prior to paying).
If no debt is present the merchant can accept or deny any form of payment at their discretion.
That's what I thought too but then I googled it.
https://www.federalreserve.gov/faqs/currency_12772.htm
There is no federal statute mandating that a private business, a person, or an organization must accept currency or coins as payment for goods or services. Private businesses are free to develop their own policies on whether to accept cash unless there is a state law that says otherwise.
Section 31 U.S.C. 5103, entitled "Legal tender," states: "United States coins and currency [including Federal Reserve notes and circulating notes of Federal Reserve Banks and national banks] are legal tender for all debts, public charges, taxes, and dues." This statute means that all U.S. money as identified above is a valid and legal offer of payment for debts when tendered to a creditor.
I’ve heard it explained that the payments of debts are through disputes in the court where a debt needs to be paid and not at point-of-sale.
