According to the United States Federal Reserve:
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.
Source: https://www.federalreserve.gov/faqs/currency_12772.htm
Are there any states, districts, regions, or territories within the USA that mandate that a private business, a person, or an organization must accept US currency or coins as payment for goods or services?