In TNG, Picard says that the Federation has evolved past a need for money. Indeed, we never see any.
In DS9 though, Quark talks a lot about bar tabs and costs. Surely O'Brien and Bashir don't get free drinks, so how do they pay? I'd assume that any Ferengi worth his lobes won't accept anything that can be replicated, so do Federation officers get a stipend of tradeable "value" when interacting with cultures that still expect payment?
I think there's also a reference to Quark paying rent to Sisko for running the bar. Presumably that's denominated in latinum. I wonder where it goes? Maybe the secret "Garak black ops" fund.
Quark doesn't pay rent for the bar, Sisco mentions this at one point when Quark is trying to sell weapons via the holodeck. Because he's annoyed with him he points out that he doesn't pay rent and he doesn't pay taxes and the federation let him get away with a lot, but there is a line.