Apex domains cannot have CNAME records.
Question and response
Question
dig greencore.co.cr. NS
Answer
greencore.co.cr. 5 NS pete.ns.cloudflare.com.
greencore.co.cr. 5 NS lucy.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0