Nobody is required to accept cash (except the issuer).
This is a problem under US and UK law: shops are required to accept cash.
In the US, that's utter bollocks. Nobody except the US Government is required to accept US currency. A friend of mine who works at "the Fed' used to occasionally have to work in customer service answering phone calls from the public. A consistent portion of calls are from people complaining that some shop, utility, landlord, school, city, state, county, or whatever won't accept cash. The callers are told that nobody except the US Government is required to accept US currency. [Even then, the hoops you have to jump through to pay your taxes in cash would kill a normal person.]