How do you make money playing FF?

I'm curious, how does one actually make money playing Final Fantasy? Is it through in-game achievements that can be traded for real-world currency? Or is there some other method, like winning tournaments or selling rare in-game items on third-party markets? I'm interested in understanding the mechanics behind it, as I've heard people can make a decent side income from playing this game. Could you elaborate on the process and how profitable it can potentially be?