GSTR-3B filing deadlines and electronic tax payment requirements were specified for monthly returns and extended taxpayers. GSTR-3B returns for January, February and March 2018 were required to be furnished electronically through the common portal by the respective due dates of 20 February 2018, 20 March 2018 and 20 April 2018. A subsequent proviso extended the filing period for taxpayers who obtained GSTIN under the specified Uttar Pradesh notification, permitting GSTR-3B returns for the period from July 2017 to November 2018 to be filed electronically on or before 31 December 2018.