Apex domains cannot have CNAME records.
Question and response
Question
dig sigmasoft.com. NS
Answer
sigmasoft.com. 2 NS ns.sigmasoft.com.
sigmasoft.com. 2 NS ns2.sigmasoft.com.
Authority
The response has no authority records.
Additional
ns.sigmasoft.com. 2 A 168.235.85.10
ns2.sigmasoft.com. 2 A 147.135.54.151
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0