Apex domains cannot have CNAME records.
Question and response
Question
dig useunica.com.br. NS
Answer
useunica.com.br. 5 NS ns-1752.awsdns-27.co.uk.
useunica.com.br. 5 NS ns-89.awsdns-11.com.
useunica.com.br. 5 NS ns-514.awsdns-00.net.
useunica.com.br. 5 NS ns-1196.awsdns-21.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0