GST Summon & Composition Scheme - Goods and Services Tax - GST

My client is a service provider and has received a summon from the CGST Authorities. Until now, he has not obtained GST registration, even though his turnover has exceeded 20 lakhs since 2020-21. I am certain that the officer will require him to obtain GST registration and pay the outstanding GST liabilities. My client s annual turnover has been around 22 lakhs from 2020-21 to 2023-24. Therefore, we are applying for registration under the Composition Scheme as per Section 10(2A) and will be paying tax at 6% . My Question: Can we apply the Composition Scheme and pay past liabilities (i.e., from 2020-21 to 2023-24) at 6% instead of the regular rate of 18% ? Can we avail such relief? or any other relief