Apex domains cannot have CNAME records.
Question and response
Question
dig bna4.vtscloud.io. NS
Answer
bna4.vtscloud.io. 5 NS ns-1251.awsdns-28.org.
bna4.vtscloud.io. 5 NS ns-1591.awsdns-06.co.uk.
bna4.vtscloud.io. 5 NS ns-47.awsdns-05.com.
bna4.vtscloud.io. 5 NS ns-848.awsdns-42.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0