Composition levy opt-out persons must pay State tax at time of supply and file returns accordingly. Registered persons who did not opt for the composition levy are notified as a class required to pay State tax on outward supply at the time of supply (per clause (a) of sub section (2) of section 12), including situations attracting section 14; they must furnish details and returns as mandated in Chapter IX and the rules, and pay tax within periods specified by the Act.