GSTR 3B filed as NIL, But Turnover is there

A user's client filed their GSTR 3B returns as NIL, even though they had a turnover between April 2019 and March 2020. They are seeking advice on how to declare this missed turnover, particularly for February and March 2020 returns which remain unfiled. The advice provided suggests amending the relevant months' returns to include the missed invoices and paying the applicable tax along with an 18% interest for the delay. If the missed invoices are for exports and thus non-taxable, interest is only applicable for the delay in tax payment.