GSTR-3B filing extension allows newly migrated taxpayers to file outstanding returns by the prescribed extended deadline. An amendment prescribes that taxpayers who obtained GSTIN under the August 2018 issuance must file returns in FORM GSTR-3B for July 2017 to November 2018 electronically through the common portal on or before the 31st day of December, 2018, by way of a proviso inserted into earlier notifications.