It's usually only obligatory to accept cash for settling a debt, e.g. if you have eaten in a restaurant, the restaurant is obliged to accept cash, because you c

It's usually only obligatory to accept cash for settling a debt, e.g. if you have eaten in a restaurant, the restaurant is obliged to accept cash, because you can hardly give back the food you already ate (at least in the same form). But if you are at McDonalds, there's no obligation for them to accept cash because you pay upfront.