Apex domains cannot have CNAME records.
Question and response
Question
dig pcrewdns.net. NS
Answer
pcrewdns.net. 5 NS ns-917.awsdns-50.net.
pcrewdns.net. 5 NS ns-2024.awsdns-61.co.uk.
pcrewdns.net. 5 NS ns-224.awsdns-28.com.
pcrewdns.net. 5 NS ns-1436.awsdns-51.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0