Money is whatever you accept on the other side of any trade. Marshall McLuhan speculated it came from our ape instinct of ‘grasp and let go’ of swinging through the trees. That instinct was adapted for trading objects. Grasp first, let go second. So, money isn’t a hallucination- it comes into existence exactly at the moment of transaction, just like a price which is exactly what someone is willing to part with at a moment in time (may not be particularly well-informed at the time).