a.ns.sinersio.com has no CNAME records.
Question and response
Question
dig a.ns.sinersio.com. NS
Answer
The response has no answer records.
Authority
sinersio.com. 225 SOA ns1.sinersio.com. postmaster.sinersio.com. 2025061102 600 600 3600000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0