Apex domains cannot have CNAME records.
Question and response
Question
dig skytap.com. NS
Answer
skytap.com. 4 NS ns-1405.awsdns-47.org.
skytap.com. 4 NS ns-453.awsdns-56.com.
skytap.com. 4 NS ns-635.awsdns-15.net.
skytap.com. 4 NS ns-1940.awsdns-50.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0