Money is not fictional. Money is a convenience that allows people to trade items that require effort to produce without the problems of barter trading. Money has been invented multiple times in various parts of the world, and its ubiquity is an indication of its utility.

The baseline value of money is human effort. That is not a concrete thing but it is by no means fictional.

If you want to have some carrots for dinner, you can grow them from seed over several weeks and finally harvest them and eat them. For free - well, the seeds have to come from somewhere - but you can allow some carrots to produce flowers and get pollinated and then you have your seeds for free too.

Or you can buy the carrots off someone else who has made the effort to produce them.