Form GSTR-3B electronic filing requirement; returns and tax liabilities must be discharged via electronic ledgers by due dates. Specifies mandatory electronic furnishing of FORM GSTR-3B through the common portal for the months listed, to be filed on or before the last dates in the Table. Requires that tax, interest, penalty, fees or any other amount declared in FORM GSTR-3B be discharged by debiting the electronic cash ledger or electronic credit ledger, subject to section 49 of the Act, not later than the last date for furnishing the return. Notes record subsequent substitutions extending the consolidated filing period for certain taxpayers.