Apex domains cannot have CNAME records.
Question and response
Question
dig nexxera.com. NS
Answer
nexxera.com. 5 NS ns-634.awsdns-15.net.
nexxera.com. 5 NS ns003.nexxera.com.br.
nexxera.com. 5 NS ns-67.awsdns-08.com.
nexxera.com. 5 NS ns-1447.awsdns-52.org.
Authority
The response has no authority records.
Additional
ns003.nexxera.com.br. 5 A 189.124.62.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0