Appointments integration with MarketPress

I've set-up appointments within marketpress and have added the quantity of available appointment slots in both the products page, as well as within Appointments. The problem is that when I go to test it, after attempting to add it to the cart, it either says, "Sorry, there is a per order limit of 1 for "Appointment", There are -1 items in the inventory, or Out of Stock within the Purchase button at the bottom.

Is there something I'm missing somewhere that's controlling the inventory of appointment?