There are two reasons why your order could be pending.

1. If you've placed a Limit Order

When you place a limit order, the order is placed and open until the scrip hits the desired price. Therefore, this is one of the reasons your order could be pending. Learn more on limit orders here .

2. When the scrip has hit the circuit limit

If there is no liquidity in the particular scrip, which means, if there are no buyers when you place a sell order, or if there are no sellers when you place a buy order, your order would be pending.