An E4 code typically indicates the unit has entered "defrost mode" because it became too cold, which may sometimes be caused by a faulty temperature sensor.
Standard cooling mode. You can manually adjust the temperature, typically between 16°C and 30°C, using the "+" and "-" buttons. Voltas Vertis Plus Split Ac User Manual
Gradually increases the set temperature by 1°C per hour (up to 2°C total) throughout the night to save energy and prevent over-cooling. An E4 code typically indicates the unit has