Apex domains cannot have CNAME records.
Question and response
Question
dig cloud-preview.vadesecure.com. NS
Answer
cloud-preview.vadesecure.com. 5 NS ns-170.awsdns-21.com.
cloud-preview.vadesecure.com. 5 NS ns-1164.awsdns-17.org.
cloud-preview.vadesecure.com. 5 NS ns-568.awsdns-07.net.
cloud-preview.vadesecure.com. 5 NS ns-1857.awsdns-40.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0