> They work globally, for values of "globally" which include "most parts of the first world which you, as someone in the middle or upper middle class, are likely to find yourself in."

For the record the same middle/upper class Westerner, if dumped in the global south, will be able to pay for things with credit cards. You can pay for some hotels in Africa with credit cards. You can pay for expensive restaurants there. You can go to an ATM and withdraw money to pay for things that need cash.