Compulsory registration under GST required for specified persons, including inter State suppliers and electronic commerce operators. The provision mandates compulsory registration for specified persons irrespective of the general registration threshold: inter State suppliers, casual and non resident taxable persons, persons liable under reverse charge or analogous tax provisions, tax deductors, agents or persons supplying on behalf of others, Input Service Distributors, electronic commerce operators, and suppliers of online information and database access services from outside India to recipients in India; the Government may notify additional persons or classes for mandatory registration.