Could easilly be a figure of speech. One thing is clear. The economics of the 24th century (where O'Brien runs up his tab) are very different to pre-new-world-economy which grew in the 22nd century. The majority of people in the Federation don't use money to grow individual wealth - wealth is grown by society, and is measured by far more than pieces of paper or promises to spend a few hours working. The 'cost' of the Enterprise E, or the 'cost' of Ayelborne's training, is as un-understandable to 80s Reaaganuts as the 'cost' of an modern aircraft carrier or a university education is to pre-agricultural people trading sharp stones for fire, at least not something you can explain in a few minutes while skulking around the ship hiding from invaders. Try explaining High Frequency Trading to Cassius Dio. Heck try explaining it to Alexander Hamilton during Yorktown.
Apparently, Gene Roddenberry came up with the "no money" rule after TOS, applying it to the "present" of TNG. The franchise's writers have tried to honor the spirit of that, more or less, while acknowledging it's a lot of nonsense and slipping in subtle references to money across the various series. It's explicitly stated in dialogue that DS9's starfleet personnel pay their bills at Quark's. ("Armageddon Game.")
Some references in dialogue might be figures of speech, just like we don't use gold as money anymore but we still have expressions like "he who has the gold makes the rules."
It makes sense to me. In their post-scarcity society the closest thing to money are credits for energy intensive products/services like transporters, holodecks, booking interstellar travel, any replicators beyond a basic food & clothes model, etc. It's probably why so many people still have part time jobs at places like Joseph Siskos restaurant.
And then the society is not post-scarcity, and does have currency, but by another name. My point is that the U.F.P. claim of such a society sans currency seems like the idle propaganda that Lilly Sloane called Picard out for.
My personal theory is that Starfleet provides a living allowance to its personnel that they can use in trade interactions with non-Federation establishments. So O'Brien, and everybody else for that matter who buys things on the promenade or uses the Holosuites simple "charges it to their account", like Dr.Crusher did in Ecnounter at Farpoint when she bought that roll of fabric. Then Starfleet compensates those non-Federation establishments by providing a resource those civilizations can't easily replicate. So in my head canon it's a special case scenario for Starfleet personnel that live among, or work closely, with societies that still have money. Their families, however don't seem to get any allowance like that, considering Jake was vocal about not having any money in a couple of episodes and that he won't get compensated for his writings. Keiko, on the other hand, might get paid by the Bajoran government for her work as a teacher and botanist.
There's no currency economy *On Earth*. But the Federation aren't strident enough to turn their noses up at cultures that still use it. So they give a stipend to crews that depend on currency economies of other cultures.
It's post-scarcity in that every one has food, clothes, shelter, education and medical care. Working voluntarily for extra credits because you want a holodeck to get freaky in or to not schlep to Paris on public transport isn't exactly slaving to keep food on the table and a roof over your head.
I guess I live in a post-scarcity society without money then. And it's not a society without currency either which is the claim the U.F.P. so often makes, but which seems to be contracted by on-screen evidence. Though never fear, such prætentious claims of states are commonplace in any era.
Wow: you live in a place with free access to all that? One with no homelessness, food insecurity, or poverty? Lucky you...
You said “shelter”, not “home”, nor did you speak of wealth. The homeless are indeed given shelter here, not a private residence of their own they might call “home”, but free stay during the night in heated facilities for the many.
My thought is that Starfleet was constantly ripping off other cultures that used money by giving them some line about "the acquisition of wealth is no longer the driving force in our lives, bye!" Like when Beverly Crusher ordered that bolt of silk at Farpoint and said to charge it to her account. When the merchant tried to charge the sale to Crusher's account, he probably found that there was no such account, and by that time the Enterprise was long gone and Crusher was somewhere out in space laughing at him, and there was nothing he could do about it. Kor
The sans currency and people working just for the enjoyment of it--peeling potatoes for example-- concepts were the most fantastical parts of the ST universe (warp drive, transporters and humans breeding with non-terran beings are much easier to believe).
So could of Picard's statement that money doesn't exist. That goes for a large number of thread topics. Doubtful, oh it's nice enough, but not post-scarcity.
Perhaps we should one day try to combine as many of these beaten-to-death topics as possible in a single question, just for the heck of it. My first shot: "Is Starfleet being funded by some military budget part of continuity or canon?"
And in "The Doomsday Machine", Kirk tells Scotty that he's earned his pay for the week after Scotty tells Kirk that he's restored one bank of phasers on the Constellation.
I will just be completely honest. I enjoy the optimistic fantasy of a society where money is no longer a deciding factor in human life. And I think 90s Trek offers enough evidence for a Human Society that functions without a currency-based and/or wealth economy. I agree that in TOS there is evidence of money and the accumulation of wealth. But that's once again one of the points were I firmly believe that the various trek shows are a "broad strokes" canon for each other.
I seem to remember Kirk saying the same thing about Chekov in one episode. However, I think it's a figure of speech. They probably aren't paid weekly, they probably don't get a financial bonus for a particularly good job, and the pay is probably just credits towards luxury items or privileges, not food or medical care.