Unable to file Annual Return for F.Y 2018 19

My client had a turnover of 50 lakhs in the year 2017 - 18.

As per notification No. 47/2019 dated 9th October, 2019 issued by CBIC, for the registered persons having aggregate turnover not exceeding 2 crores, filing of GSTR 9 was made optional.

So, I did not file the annual return of the said client for 2017 - 18.

The same client had a turnover of 4 crores in 2018 -19 and today when I tried to file his annual return for the said year, it says you can't file unless you file annual return for the previous year, ie; 2017 18 , with penalty of course as its past the due date..

What's the solution here?