the coin itself is not important if its not backed up by either its value in some other commodity(like gold, when the gold standard was still a thing) or the promise of economic staiblity of the entitiy issuing the coin(essentially guaranteeing you at you can at any time exchange said coin for its value on the respective currency)

the1st requires that you actually have said commodity in stock ready ot exchange, whiel the latter requires that your nation has the economic might to be good on this promise else i will not trust that coin.