A good read on Currency, Fiat and some food for thought. https://www.newyorker.com/magazine/2019/08/05/the-invention-of-money? The problem with many new forms of money is that people are reluctant to adopt them. Genghis Khan’s grandson didn’t have that difficulty. He took measures to insure the authenticity of his currency, and if you didn’t use it—if you wouldn’t accept it in payment, or preferred to use gold or silver or copper or iron bars or pearls or salt or coins or any of the older forms of payment prevalent in China—he would have you killed. This solved the question of uptake. These days, the death is economic, but the principle remains.