GST SALES IN IT RETURN

Octo 17 to march 18 gst sales was 6 lakhs in GST return and total sales 17 / 18 is 12 lakhs than in IT return And in P/L as a gross sales what to show 6 lakhs or 12 lakhs? Before gst there was not vat no... Means sales in P/L 12 lakhs and in IT RETURN gst turnover 6 laks....