sigma.validns.com has no CNAME records.
Question and response
Question
dig sigma.validns.com. NS
Answer
The response has no answer records.
Authority
validns.com. 492 SOA dns1.validns.com. servers.validns.com. 2026021405 7200 7200 3600000 992
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0