Apex domains cannot have CNAME records.
Question and response
Question
dig grupoacciona.pre.ivcert.net. NS
Answer
grupoacciona.pre.ivcert.net. 5 NS ns-686.awsdns-21.net.
grupoacciona.pre.ivcert.net. 5 NS ns-1814.awsdns-34.co.uk.
grupoacciona.pre.ivcert.net. 5 NS ns-328.awsdns-41.com.
grupoacciona.pre.ivcert.net. 5 NS ns-1353.awsdns-41.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0