Apex domains cannot have CNAME records.
Question and response
Question
dig acciona-energia.pro.ivcert.net. NS
Answer
acciona-energia.pro.ivcert.net. 5 NS ns-467.awsdns-58.com.
acciona-energia.pro.ivcert.net. 5 NS ns-832.awsdns-40.net.
acciona-energia.pro.ivcert.net. 5 NS ns-1093.awsdns-08.org.
acciona-energia.pro.ivcert.net. 5 NS ns-1839.awsdns-37.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0