Difference in liability

A user mistakenly entered less output and input tax for August 2017 in GSTR 3B, though GSTR 1 was filed correctly. The difference was later adjusted in September 2017. Now, they've received a notice regarding the liability difference between GSTR 3B and GSTR 1 and are seeking advice on how to respond, specifically by explaining the adjustment made in the following month and providing supporting documentation.