Apex domains cannot have CNAME records.
Question and response
Question
dig grupconexio.com. NS
Answer
grupconexio.com. 5 NS ns-843.awsdns-41.net.
grupconexio.com. 5 NS ns-704.awsdns-24.net.
grupconexio.com. 5 NS ns-2040.awsdns-63.co.uk.
grupconexio.com. 5 NS ns-1241.awsdns-27.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0