Apex domains cannot have CNAME records.
Question and response
Question
dig entorno.es. NS
Answer
entorno.es. 5 NS ns2.entornodns.com.
entorno.es. 5 NS ns1.entornodns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0