GSTR-3B Filing Deadline set for monthly returns; electronic payment via cash or credit ledger required. FORM GSTR-3B for October 2019 to March 2020 must be furnished electronically through the common portal on or before the twentieth day of the month succeeding each month. Tax liabilities declared in FORM GSTR-3B must be discharged by debiting the electronic cash ledger or electronic credit ledger, as applicable, not later than that same due date.