Apex domains cannot have CNAME records.
Question and response
Question
dig stg-apse2.docebomail.com. NS
Answer
stg-apse2.docebomail.com. 5 NS ns-806.awsdns-36.net.
stg-apse2.docebomail.com. 5 NS ns-259.awsdns-32.com.
stg-apse2.docebomail.com. 5 NS ns-1763.awsdns-28.co.uk.
stg-apse2.docebomail.com. 5 NS ns-1253.awsdns-28.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0