Apex domains cannot have CNAME records.
Question and response
Question
dig cgralcolea.es. NS
Answer
cgralcolea.es. 5 NS macy.ns.cloudflare.com.
cgralcolea.es. 5 NS gabe.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0