IMHO the premise of Star Trek economy is that all needs of an ordinary person can be fulfilled so cheaply it doesn't make sense to meter. The replicator uses a relatively minimal amount of energy. They still need to allocate resources - and even trade them among themselves and with others - but there's no need for an internal currency, they can power entire planets with their antimatter reactors using just a very small amount of fuel. Even the starships that are bending spacetime itself all the time are refueled only very occasionally, synthesizing some food and houses is nothing compared to that.

The only time when their economy breaks is when they're in an active warzone - and frankly, currency as we know it breaks down in a warzone too, you better have some cigarettes, food or weapons if you want to trade.