Return filing obligation in FORM GSTR-3B: monthly deadlines and mandatory ledger-based tax payment by specified last dates. Mandates furnishing of returns in FORM GSTR-3B for January, February and March 2018 through the common portal by the specified last dates, and requires that declared tax liabilities be discharged by debiting the electronic cash ledger or electronic credit ledger, as applicable, not later than those corresponding last dates.