Apex domains cannot have CNAME records.
Question and response
Question
dig cti.com.br. NS
Answer
cti.com.br. 4 NS dns1.ctitech.net.br.
cti.com.br. 4 NS dns3.ctitech.net.br.
cti.com.br. 4 NS dns2.ctitech.net.br.
cti.com.br. 4 NS dns4.ctitech.net.br.
Authority
The response has no authority records.
Additional
dns1.ctitech.net.br. 4 A 177.190.207.234
dns2.ctitech.net.br. 4 A 186.193.234.22
dns3.ctitech.net.br. 4 A 186.193.225.228
dns4.ctitech.net.br. 4 A 104.251.215.11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0