Furnishing of returns: registered persons must file prescribed electronic returns timely and pay due tax alongside the return. Section 39 mandates electronic filing of returns by specified classes of registered persons with distinct deadlines, requires inclusion of inward and outward supplies, input tax credit, tax payable and tax paid, and mandates payment of tax due by the return filing date. The Commissioner may extend filing deadlines by notification. Returns must be filed for every tax period including nil periods; rectification of omissions or incorrect particulars in subsequent returns is allowed subject to interest and time limits, and filing for a tax period is barred if previous periods' returns remain outstanding.