That's legal. https://www.federalreserve.gov/faqs/currency_12772.htm
Legal tender applies only to debt/creditor relationships.
> Legal tender is a form of money that courts of law are required to recognize as satisfactory payment in court for any monetary debt.
A country may separately require businesses to accept legal tender, if they feel like it.
https://en.wikipedia.org/wiki/Legal_tender#Status_by_country would appear to indicate this distinction is very common in the developed world.
That's legal. https://www.federalreserve.gov/faqs/currency_12772.htm
Legal tender applies only to debt/creditor relationships.