Under Invest option, in cash segment you are only allowed to sell what you have in your demat account.
If you wish to do a short sell, you can do so using our two intraday products MIS and Cover Order
How do I modify or cancel an order?
Can I place a limit order as AMO?
What are the order types available and where do I find them?
For cover orders, till what time can I square off my open positions manually?