Why does an order get rejected?

Order rejections in Indian equity and F&O trading usually trace back to one of a handful of causes: insufficient margin or funds for the order value, a price entered outside the exchange’s circuit limit or price band for that stock, an invalid order type or quantity for that segment (like placing an odd lot in a segment that doesn’t allow it), a technical issue like a stale session or connectivity drop, or a compliance block, such as trying to trade a stock under an exchange-imposed restriction like an F&O ban period. Each rejection comes with a specific reason code or message from the exchange, which you check first rather than guessing, since the fix is different depending on the cause: topping up margin is different from adjusting the price to fit the circuit band. If the rejection message is unclear, you check the order book for the exact reason before retrying, so you don’t repeat the same mistake.