All you have to do is look at prisons as a good example, standard currency is tightly controlled, typically not very available to inmates and somewhat pointless

All you have to do is look at prisons as a good example, standard currency is tightly controlled, typically not very available to inmates and somewhat pointless to inmates anyway. So alternative currencies are used. Drugs, cigarettes, food, weapons, personal hygiene stuff, people, the list goes on. Currency is only as meaningful as its usefulness to people. If a large number of people can't or won't use a currrency, they'll just find another. It wouldn't be the first time in history a majority currency became too inconvenient for a large number of people and alternatives were found.