Apex domains cannot have CNAME records.
Question and response
Question
dig opalstack.com. NS
Answer
opalstack.com. 5 NS ns3.us.opalstack.com.
opalstack.com. 5 NS ns1.us.opalstack.com.
opalstack.com. 5 NS ns2.us.opalstack.com.
Authority
The response has no authority records.
Additional
ns1.us.opalstack.com. 5 A 45.79.107.55
ns2.us.opalstack.com. 5 A 23.92.21.232
ns3.us.opalstack.com. 5 A 45.56.74.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0