The question of the economics of the future arises regularly. After discussing it regularly for years, I'm struck by how resistant to the claims of "no money" some fans are. Warp drive, transporters and phasers are all readily accepted, despite the violations of known physics, because fans can accept the possibility of future breakthroughs in sciences that might
make such things possible.
But no money? Impossible! Why the inability to accept the possibility? Is it because people think they understand economics better than they understand physics, so they can't imagine an economic system that isn't exactly what we use today? Economics without money shouldn't be harder to accept than warp drive.
I read a book by Charles Stross where a new economic system, referred to as Economics 2.0, was used by a new transhuman society. It was completely incomprehensible to the merely human characters of the story. Whatever economic system the Federation uses, I imagine it as something unfamiliar to us and unique to the future of Star Trek, something complex that developed over time as the Federation tied its member societies closer together.