Hi sorry for late reply, I will have a look at this when I get a chance, which may not be until Monday as I am away for a couple of days. Are you trying to deploy the Marketplace under a roof or near an overhanging building? It also checks for nearby deployable, spawned and static entities. So it it is too near to any trash piles, barrels, crates etc it wont place. The plugin checks the area to make sure the entire structure can be placed.
Also, make sure you are not trying to place it too near to yourself. Try and place it further away from you and see if that helps you.
Without testing it myself I can't help you further and will do so as soon as I can, thanks for your understanding.