Apex domains cannot have CNAME records.
Question and response
Question
dig online.dev.br. NS
Answer
online.dev.br. 3 NS ns2.online.dev.br.
online.dev.br. 3 NS ns.online.dev.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0