Free energy, vast reserves of raw materials from the asteroids, nanotechnology factories, cheap and quick access to entertainment and knowledge -- by the middle of the Twenty-First Century, mankind was in an economy of abundance. The most valuable commodity was service.
While it was possible for a citizen to exist without working at all, a small additional effort could reap great rewards. But how to engage in commerce when gold could be winnowed out of seawater? What kind of money could you use when a counterfeiter could photocopy any currency?
Ever more complex systems of barter, rare commodity-backed currency, or oaths of exchange were tried. Emperor Heinlein brutally enforced an absolute prohibition against the importation of gold, jewels, or most manufactured goods.
A refugee from a Strange World Yellow reality that had diverged in 1952 had a solution. It wasn't perfect, and made as many people unhappy as were happy, but nobody could come up with a better idea.
The new pseudo-dollar would be worth one hour of manual labor. Pseudo-dollars would reside in identical finance cards, one card to each citizen. New pseudo-dollars were accrued upon evidence of the requisite manual labor. Funds could also be transferred from one finance card to another. Only a card touched by the owner could approve such a transfer.