it is mandatory for the builder or developer to obtain an Occupancy Certificate before selling any apartment or flat in the building. So, a flat cannot be sold or occupied without an Occupancy Certificate. Moreover, it can be considered as illegal to buy a flat without OC.
Obtaining an OC is a requirement under the Karnataka Apartment Ownership Act, 1972. The law says one cannot legally move into a building unless the developer gets an occupancy certificate from the BBMP or BDA. The corporation can ask apartment owners to leave such illegally occupied flats or impose heavy penalties.
Without an OC, the authorities can disconnect the water connection, sewer connection, or electrical supply without notice. Your building may be dismantled if it lacks a valid OC since it is classified as an illegal structure. The OC is essential when applying for a home loan or a loan to buy a resale unit.