You have to pay maintenance on the units you levy.A warrior costs 40 production so if a CS has 3 warriors to Levy, it will cost 120 gold to do so. It costs the base production value of the units levied in gold.You can do this multiple times for each CS but if already levying units, you cannot levy more until you are no longer levying units. You can levy a City States (CS) military units if you are currently suzerain of that CS.
