Apex domains cannot have CNAME records.
Question and response
Question
dig labplus.net.do. NS
Answer
labplus.net.do. 1 NS dns3.midominio.do.
labplus.net.do. 1 NS dns4.midominio.do.
labplus.net.do. 1 NS dns1.midominio.do.
labplus.net.do. 1 NS dns2.midominio.do.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0