Why is an order rejected despite having sufficient funds?

Having enough cash balance doesn’t automatically mean the order has enough margin, and this trips up a lot of traders, especially in F&O. For intraday and F&O trades, brokers block a specific margin amount (which can include SPAN margin, exposure margin, and sometimes additional broker-level buffers) that may be higher than the simple trade value, and if your available margin (after accounting for other open positions) falls short, the order gets rejected even with cash sitting in the account. Other non-fund reasons include the stock being in an exchange-imposed trading restriction, the order price falling outside the circuit limit, or a technical mismatch like an expired session token. You check the specific margin required for that order (shown in the order window before confirmation) against your available margin, not just your total account balance, since those two numbers aren’t the same thing.