account_id is your user_id (6-digit identification code at Zerodha). placed_by is the ID from where your order was placed. This field will have your account_id for all orders you place directly. When Zerodha's RMS system places orders, it will carry the RMS dealer IDs. This can be for MIS square-off orders after 3.20 PM, margin shortfall square-offs, etc.
account_idis youruser_id(6-digit identification code at Zerodha).placed_byis the ID from where your order was placed. This field will have youraccount_idfor all orders you place directly. When Zerodha's RMS system places orders, it will carry the RMS dealer IDs. This can be for MIS square-off orders after 3.20 PM, margin shortfall square-offs, etc.