GST returns filing requirement: electronic submission, payment timing, rectification limits and filing restrictions clarified. Section 39 mandates electronic returns filing for registered persons, detailing who must file, required return content (inward and outward supplies, input tax credit, tax payable and paid), periodicity (monthly, quarterly or annual as prescribed for specific classes), distinct obligations for Input Service Distributors, non-resident taxpayers and TDS deductors, the timing of tax payment with returns, permitted rectification of omissions subject to interest and cut-off limits, restrictions on filing where prior-period returns or outward-supply details are outstanding, and a three-year limitation on filing except where notified otherwise.