One thing that usually comes up in invented fantasy worlds, even if just in passing, is the need to exchange money for good and services.
Rare is the story where you can focus on a strange way to do it – most of the time is it little more than colour. Worlds based on Dungeons and Dragons usually have “gold pieces” as the core value (often abbreviated to “gp”) plus lesser values in silver and copper. Which is kind of ironic because the original idea of “gold piece” was so that game writers could create some local colour by changing the name. Many don’t, of course.
It also ignores some of the economic history of our own world. In medieval Europe, which is the basis for a lot of fantasy fiction world-building, the average man-in-the-field never ever saw gold in his entire life. Gold was rare and thus highly valuable. Too valuable, in fact: silver was much less rare and so many coins were struck in silver. But even a single English silver penny was worth a lot: Wikipedia tells us that estimates of its equivalent value in today’s terms is something like $20. That tells us that a lot of local trade wasn’t transacted with money. No wonder few people ever saw gold.