Filing of GSTR-3B returns: monthly deadlines and mandatory electronic ledger discharge for declared tax liabilities. Returns in FORM GSTR-3B for August through December 2017 must be filed electronically by the last dates specified for each month, and registered persons must discharge tax, interest, penalty, fees or other amounts declared in GSTR-3B by debiting the electronic cash ledger or electronic credit ledger, as applicable, not later than those respective filing dates.