Apex domains cannot have CNAME records.
Question and response
Question
dig sardinasystems.com. NS
Answer
sardinasystems.com. 5 NS e.ns.sardinasystems.com.
sardinasystems.com. 5 NS a.ns.sardinasystems.com.
sardinasystems.com. 5 NS c.ns.sardinasystems.com.
sardinasystems.com. 5 NS b.ns.sardinasystems.com.
sardinasystems.com. 5 NS d.ns.sardinasystems.com.
sardinasystems.com. 5 NS f.ns.sardinasystems.com.
Authority
The response has no authority records.
Additional
a.ns.sardinasystems.com. 5 A 37.187.129.184
b.ns.sardinasystems.com. 5 A 94.159.109.217
c.ns.sardinasystems.com. 5 A 159.195.70.148
d.ns.sardinasystems.com. 5 A 192.95.33.91
e.ns.sardinasystems.com. 5 A 193.162.143.15
f.ns.sardinasystems.com. 5 A 194.36.178.148
a.ns.sardinasystems.com. 5 AAAA 2001:41d0:a:3eb8:0:0:0:1
b.ns.sardinasystems.com. 5 AAAA 2a0b:4142:cb5:0:0:0:0:2
c.ns.sardinasystems.com. 5 AAAA 2a0a:4cc0:c2:273e:0:0:0:a
d.ns.sardinasystems.com. 5 AAAA 2607:5300:60:305b:0:0:0:1
e.ns.sardinasystems.com. 5 AAAA 2a09:5302:ffff:0:0:0:0:cc0
f.ns.sardinasystems.com. 5 AAAA 2a04:5201:8018:0:0:0:0:65
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0