Relations Between Union and States
(1) With a State government's consent, the President may entrust it (or its officers) with functions relating to Union executive power matters. (2) A Parliament law applicable in a state may confer powers/duties on the state or its officers even on matters the state legislature couldn't itself legislate on. (3) Where this happens, the Union must pay the state any agreed (or arbitrator-determined) extra administrative cost involved.
This allows practical, cooperative delegation: the Union can hand over administration of certain Union-subject functions to a willing state government (with the state's consent) rather than the Union having to build its own separate administrative machinery in every state, again with cost reimbursement built in.
This is why certain Union-subject functions are sometimes actually administered day-to-day by state government officials on the Union's behalf, rather than the central government needing entirely separate field offices and staff in every state for that purpose.