Apex domains cannot have CNAME records.
Question and response
Question
dig aws.vtscloud.io. NS
Answer
aws.vtscloud.io. 5 NS ns-494.awsdns-61.com.
aws.vtscloud.io. 5 NS ns-913.awsdns-50.net.
aws.vtscloud.io. 5 NS ns-1031.awsdns-00.org.
aws.vtscloud.io. 5 NS ns-1885.awsdns-43.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0