Apex domains cannot have CNAME records.
Question and response
Question
dig inumbo.net. NS
Answer
inumbo.net. 5 NS ns-649.awsdns-17.net.
inumbo.net. 5 NS ns-1844.awsdns-38.co.uk.
inumbo.net. 5 NS ns-84.awsdns-10.com.
inumbo.net. 5 NS ns-1423.awsdns-49.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0