well the question is debt really. I know places can accept payment as they chose but for payment of debt is what I recollect of the law. I don't recall that law for allowing the reciever to be picky about the form of the currency. Granted the debt payer has to get the payment in and if they just don't have a physical presence for it you can't just leave it on the floor and say debt paid. It is certainly a confusing issue but an important one as such requirements are part of why fiat currency is valueless. that along with the taxing body and just the theoretical value the country holds .