Apex domains cannot have CNAME records.
Question and response
Question
dig iset.com.br. NS
Answer
iset.com.br. 5 NS ns-707.awsdns-24.net.
iset.com.br. 5 NS ns-1440.awsdns-52.org.
iset.com.br. 5 NS ns-2020.awsdns-60.co.uk.
iset.com.br. 5 NS ns-426.awsdns-53.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0