Marking a spot as unavailable is great if you have a spot that is normally open but is either reserved (on a regular basis) or is out of service but you'd like clients to know they will still be next to a bike etc.
Go to "Settings --> Locations"
Tap into location
Edit room
4. Once in the room, double click on the spot that you want to make unavailable.
5. "Mark as unavailable" and click "save spot"