Apex domains cannot have CNAME records.
Question and response
Question
dig altostratus.co. NS
Answer
altostratus.co. 5 NS ns3.altostratus.co.
altostratus.co. 5 NS ns2.reflex.co.za.
altostratus.co. 5 NS ns1.reflex.co.za.
Authority
The response has no authority records.
Additional
ns3.altostratus.co. 5 A 52.57.24.138
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0