Create an open order. Limit orders (LMT) require price. Market orders (MKT) do not require price and are submitted as IOC. Stop-limit orders (STL) require price, trigger_price, and GTC time_in_force. A buy stop triggers when mark price reaches or exceeds trigger_price; a sell stop triggers when mark price reaches or falls below trigger_price. Mark price is the median of the best bid, best ask, and last trade. A stop order is initially active, is not on the order book, and reserves the required funds. After triggering, it behaves as a GTC limit order and can become booked or filled. Buy trigger prices are rounded up and sell trigger prices are rounded down to the product tick size. The limit price must be below 125% of trigger_price for buys or above 80% for sells.