When you exit positions, the order window may show margin required because closing that position will increase your utilised portfolio margin by that amount. Your order will execute regardless of the margin required displayed.
If the margin required field shows a value other than 0 while you exit an existing position, check for pending orders on Kite by visiting kite.zerodha.com/orders.
When exiting positions, the order window may show the margin required, indicating that closing the given leg will increase the utilised portfolio margin by that amount. The order will go through irrespective of the margin required displayed.