Apex domains cannot have CNAME records.
Question and response
Question
dig stg-cac1.docebomail.com. NS
Answer
stg-cac1.docebomail.com. 5 NS ns-779.awsdns-33.net.
stg-cac1.docebomail.com. 5 NS ns-1884.awsdns-43.co.uk.
stg-cac1.docebomail.com. 5 NS ns-158.awsdns-19.com.
stg-cac1.docebomail.com. 5 NS ns-1500.awsdns-59.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0