Apex domains cannot have CNAME records.
Question and response
Question
dig umbraco.io. NS
Answer
umbraco.io. 5 NS kara.ns.cloudflare.com.
umbraco.io. 5 NS stan.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0