Apex domains cannot have CNAME records.
Question and response
Question
dig sitebuilder-fx.com. NS
Answer
sitebuilder-fx.com. 5 NS ns-569.awsdns-07.net.
sitebuilder-fx.com. 5 NS ns-513.awsdns-00.net.
sitebuilder-fx.com. 5 NS ns-1737.awsdns-25.co.uk.
sitebuilder-fx.com. 5 NS ns-1145.awsdns-15.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0