Liquidity
Liquidity is how much money is available to match at a given price on an exchange. Thin liquidity means a large lay may not be matched at that price.
On an exchange, a price is an offer from other users and holds only for the money they have put up at it. Liquidity is that money. A busy market has plenty at several prices close together, while a quiet one may show a single small offer, so the price on screen and the price a stake gets can differ.
Say a lay stake of 20 units is needed and the best lay price, 3.1, has 12 units available. The first 12 match at 3.1 and the other 8 either wait unmatched or go at the next price, say 3.2, where each unit laid carries a liability of 2.2 instead of 2.1. Until the rest matches, the position is only part covered. Once it does, the lay stake worked out for 3.1 has been partly laid at 3.2, so the two outcomes no longer cost the same and the qualifying loss grows on one side.
In the OddsRelay feed
In the feed, liquidity is lay[].available, the money available at that lay price, on every matched offer, with lay sorted lowest price first. Raw carries available beside each exchange's lay_price by default, and includeLiquidity=false leaves it out. meta.last_seen gives each exchange's last read per sport, so a tool knows how old the figure is.
Each-way and extra-place carry it twice, on lay.win and on lay.place. Those are separate exchange markets with their own money, so a place lay can be short of liquidity while the win lay is not, and an each-way pair is only as coverable as its thinner half.
The matched feeds are gated on lay liquidity, so a pair appears only where the exchange side has money behind it. The gate cannot know any user's stake. Comparing the lay stake a tool has worked out with available, and warning when it does not fit, stays with the tool.
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