Apex domains cannot have CNAME records.
Question and response
Question
dig astrumnival.com. NS
Answer
astrumnival.com. 5 NS opr-ns3.astrumnival.com.
astrumnival.com. 5 NS opr-ns2.astrumnival.com.
astrumnival.com. 5 NS opr-ns1.astrumnival.com.
Authority
The response has no authority records.
Additional
opr-ns1.astrumnival.com. 5 A 195.211.130.10
opr-ns2.astrumnival.com. 5 A 195.211.129.1
opr-ns3.astrumnival.com. 5 A 195.211.129.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0