Optional annual return filing for small taxpayers; portal accepts filings only before the due date, voluntary payment permitted. Optional annual return filing is permitted for small taxpayers for FY 2017-18 and 2018-19: composition taxpayers may optionally file FORM GSTR-9A and other eligible registered persons may optionally file FORM GSTR-9, but such filings must be done on or before the due date since the common portal will not permit filing for those periods after the due date. Taxpayers discovering short payment or ineligible input tax credit may voluntarily self-ascertain and pay via FORM GST DRC-03.