missed invoice in GSTR1

GST CENTRE (92 Points)

24 August 2018  
Dear Experts,
For FY 2017-18 few of our sales bills are not filed in GSTR1. while reconciliation of GSTR 2A by our customer, he is asking to file their bills.
is it possible that missed sales invoices can be filed in August month return?

or while filing GSTR 2 let customer can upload the invoice so that we can accept it.

how to solve this? please guide us.

Thank you in advance.