GST return filing obligations require periodic electronic returns and timely tax payment, with extensions possible by notification. Section 39 requires registered persons to furnish prescribed electronic returns at specified periodicities and deadlines according to taxpayer category, mandates payment of tax by the return due date, authorises the Commissioner to extend deadlines by notification, requires filing for every tax period including nil periods, permits rectification of omissions or incorrect particulars in subsequent returns subject to interest and timing limits, and bars filing for a period when earlier period returns are outstanding.