DIFFERENCE BETWEEN 26AS AND GST TURNOVER

sir

My client sell his product on Amazon from which his turnover for the year is 27 lakhs and this is match between GSTR-1 ,GSTR-3B and the sell show by amazon in tcs return which they deducted TCS in gst.
But in 26as they show total sales of Rs.35 lakhs on which they deducted tds u/s 194-O when I ask them about the difference they reply that the tds of 94o is deducted on total sales including sales return made during the year.

Kindly guide me if show my turnover as per gst than there is difference in 26as and gst turnover is there chances of getting notice from IT Deptt.