I guess it could be like : UserA deposits 140k USDT and place buy order @14k tzBTC 140k > locked into contract wallet > add to Buy orderbook @14k UserB add 10BTC to sell @14k with same process A contract lookup if there’s already a buy order BTC@14k, if exist w/ quantity >= 10 then : send 10 BTC to UserA && unlock 140K > send back to UserB. If it’s only 5BTC added up then 70k will remain on orderbook and locked in contract wallet until another order add up to check 🤷♂️