Apex domains cannot have CNAME records.
Question and response
Question
dig popvertizerserving.net. NS
Answer
popvertizerserving.net. 5 NS ns-1940.awsdns-50.co.uk.
popvertizerserving.net. 5 NS ns-1510.awsdns-60.org.
popvertizerserving.net. 5 NS ns-358.awsdns-44.com.
popvertizerserving.net. 5 NS ns-835.awsdns-40.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0