SCN U/S-73

Respected Members, 

   I have received a SCN -73, for one of my client.

Actually Taxable Value and  Tax amount was shown in GST-1 for the Period April -June 2021. and the GST was also paid within the time. 

But mistakenly we have not shown the GST amount in GST-3B, and the same was not shown for the F.Y. 2021-22. 

Now Department has sent a Notice SCN. -73. So what is solution for the same. 

Thanks