Apex domains cannot have CNAME records.
Question and response
Question
dig negociarmensalidade.com.br. NS
Answer
negociarmensalidade.com.br. 5 NS ns12.wixdns.net.
negociarmensalidade.com.br. 5 NS ns13.wixdns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0