Apex domains cannot have CNAME records.
Question and response
Question
dig grupoacciona.pro.ivcert.net. NS
Answer
grupoacciona.pro.ivcert.net. 5 NS ns-895.awsdns-47.net.
grupoacciona.pro.ivcert.net. 5 NS ns-1352.awsdns-41.org.
grupoacciona.pro.ivcert.net. 5 NS ns-1877.awsdns-42.co.uk.
grupoacciona.pro.ivcert.net. 5 NS ns-183.awsdns-22.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0