GSTR 9 MARCH 2021

Turnover of Rs 10 lakhs pertaining to FY 2020-21 was omitted to be reported in gstr1 and 3b for FY 2020-21. It was wrongly shown as sales in May 2021 and the output tax was paid in May 2021. How to rectify it. Please help. I think GSTR9 can be filed now . But whether there will be any tax liability that the assesee has to pay. Whether the wrongly disclosed turnover in May 2021 can be reversed and the tax paid in May 2021 can be used to set off the GSTR9 liability.

Please Guide