If you bring cash that value is set by a third party
This based on the wrong idea that "cash" has some universally defined value. It doesn't. "Cash" is just a moniker for some good that you trade for another good. The valuation is done at the moment of exchange only and valid only for the persons taking part in that exchange,
Hopefully that good is actual money, i.e. some hard metal.
Today, "cash" is cheap paper and symbols in computer memories.
If you are the government, the value of that kind of "cash" is basically zero (the cost of a print run) and you can buy anything at all. If you are the seller-to-government, you will make sure you increase the price before you are being handed that paper and then you will spend it pretty fast (transforming it into money) if you know what is good for you.
"Legal recognition" is bullshit front, back and center as the Weimar hyperinflation nicely showed.