Sherloque seemed to have little trouble paying debts on one earth with money earned on another one.
Either there is an inter-dimensional currency exchange, somewhere, or Wells wants some of his wives dragged to prison as counterfeiters.
The secretary of the treasury has to be the same person, signing the notes into legal tender, across 5 worlds, and the historical figures painted on the front have to be from the same histories, the serial numbers can't be waaa-aay off, and the ink, which in itself is a combination to confuse counterfeiters have to be almost exactly the same, and as if any one Rene Adler doesn't come from a cowboy world or a post apocalypse where any one even remembers/knows how to put holograms onto cash, and the magnetic strips!
Sigh.
Remember that time on Sliders, in the pilot maybe, where they try to buy a hot dog with greenbacks, but the accepted currency was redbacks, becuase America was a commie.