What is gstr 1a?

gstr 1a is the return which shows the invoices modified , rejected or newly added missing invoices by the counter party in their gstr 2 

gstr 1a is auto - populated and due date 02-11-2017

but as the due date for gstr 2 for the m/o JULY has been extended 30-11-2017 so GSTR 1a will be filed after gstr 2 so wait for due date of gstr 1a 

how to file go here :: https://www.caclubindia.com/share_files/how-to-file-gstr-1a-gst--74480.asp