Apex domains cannot have CNAME records.
Question and response
Question
dig mgnhost.com. NS
Answer
mgnhost.com. 5 NS ns1.mgnhost.com.
mgnhost.com. 5 NS ns3.mgnhost.com.
mgnhost.com. 5 NS ns2.mgnhost.com.
Authority
The response has no authority records.
Additional
ns1.mgnhost.com. 5 A 185.149.194.2
ns2.mgnhost.com. 5 A 193.0.178.25
ns3.mgnhost.com. 5 A 193.233.72.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0