Please refer section 25 ss 1of Cgst .also refer section 22 and 24 regarding the turnover for registration..and if u r not eligible in T/o..then u can take voluntary registration under section 25 ss 3
As per the Provision of Section 22 of the CGST Act 2017, A person is required to take Registration under GST if his Aggregate Turnover exceeds Rs. 20 lakhs.
Also as per the Provision of Section 24 of the CGST Act 2017, Persons dealing in INTER STATE OUTWARD SUPPLY OF GOODS or SERVICES are required to take GST Registration mandatorily irrespective of any turnover threshold limit. But a relief has been given to the Supplier of Services dealing in Inter State Supply, that they will be required to take registration under GST only when their Aggregate Turnover exceeds Rs. 20 lakhs.
And you can also take Registration under GST "VOLUNTARILY" by virtue of Section 25(3) of the CGST Act 2017.
The turnover threshold limit of Rs. 40 lakhs is applicable only for the Suppliers who deal in "EXCLUSIVE SUPPLY OF GOODS", as per Notification No. 10/2019 - Central Tax, dated 07th March 2019. It became effective from 01/04/2019.
Since you are a Service Provider, so the limit of Rs. 40 lakhs will not be applicable for you.