Why are option orders rejected?

Common causes include insufficient margin for the specific contract (which can be substantial for option selling, much less so for buying), attempting to place an order for a contract that’s outside the current circuit or price band, trying to trade a contract close to or past its trading cut-off near expiry, or a lot size mismatch where the quantity entered isn’t a valid multiple of the exchange-set lot size. Illiquid strikes, especially deep out-of-the-money or far-dated options with very low trading volume, can also see order rejections or extreme slippage even when technically valid, simply because there isn’t enough market depth to match the order. You check the specific rejection message first, since margin shortfall, an invalid lot quantity, and a stock under F&O trading restriction each require completely different fixes.