How to enable product quantity feature in free version of sharetribe?

I want to enable add quantity per product in my free version of sharetribe code. So can i enable that.

I think quantity feature is included in free version because i found column of quantity in database.

listings :-

t.string   "quantity"
t.string   "quantity_selector"

transactions :-

t.integer  "listing_quantity"

listing_units :-

t.string   "quantity_selector"

So how can i display quantity during listing and during buying item ?