Real-time order book updates for a specific instrument.
[action, price, amount], where action is one of: new, change, delete.Each notification includes a change_id. Every message except the first also contains prev_change_id. If prev_change_id equals the change_id of the previous message, it indicates that no messages were missed.
Units: For perpetuals and futures, amount is in USD units. For options, amount is in the corresponding cryptocurrency contracts (e.g., BTC or ETH).