Zerodha sends a voice message and an email notifying the clients to transfer sufficient funds by 11:59 PM if there's a margin shortfall in their account. Margin shortfall means a shortage of funds or margin in the trading account.

Exchanges require clients to maintain sufficient margins in their accounts for the trades they take. Even if the required margins are collected when entering a trade, there is still a possibility of having a margin shortfall for the following reasons:

1. Exiting hedged positions: There will be a margin shortfall if the client exits a position which provides the margin benefit in a hedged trade, thereby increasing the required margin. To learn more, see Can exiting one leg of a hedged position lead to a peak margin shortfall?
2. Expiry of one of the hedged positions: The required margin may increase if one or more contract in the hedged portfolio gets expired. This is because the hedge may break, causing the margin benefit to be lost, resulting in a margin shortfall.
3. Change in overall portfolio margin: Buying or selling one or more positions might lead to a change in overall portfolio margins resulting in margin shortfall.
4. Volatility: The minimum margin required to hold a position might increase because of intraday volatility leading to a margin shortfall.

To know why funds should be added to cover margin shortfalls, see Why should clients transfer funds to cover margin shortfalls?