Apex domains cannot have CNAME records.
Question and response
Question
dig acciona-energia.pre.ivcert.net. NS
Answer
acciona-energia.pre.ivcert.net. 5 NS ns-584.awsdns-09.net.
acciona-energia.pre.ivcert.net. 5 NS ns-96.awsdns-12.com.
acciona-energia.pre.ivcert.net. 5 NS ns-1658.awsdns-15.co.uk.
acciona-energia.pre.ivcert.net. 5 NS ns-1025.awsdns-00.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0