There may be three reasons why you are unable to exit your position.
1. You already have an open order on that holding. You will need to cancel the first open order before placing another one.
For example: You have +100 position in an F&O contract (100 quantity bought) with an open exit order at SL, or a limit order of the same contract for 100 quantity. Now, if you place an exit order at market price, it might get rejected because this second exit order will be treated as a new short position you are trying it create. You would require significantly higher margin. You need to cancel your open order and place the exit order at market price again.
2. As per Groww's risk policy, for a stock option, you cannot exit or take a fresh postion after 10 AM on the expiry day of that particular option. Your existing positions will be squared off automatically after 10 AM.
3. The stock you are trying to buy has already hit the day's circuit. You can check the day's circuit (low and high range) on the order card.