Apex domains cannot have CNAME records.
Question and response
Question
dig grupotrc.com. NS
Answer
grupotrc.com. 5 NS ns6.gnet.es.
grupotrc.com. 5 NS ns3.gnet.es.
grupotrc.com. 5 NS ns4.gnet.es.
grupotrc.com. 5 NS ns5.gnet.es.
Authority
The response has no authority records.
Additional
ns3.gnet.es. 3 A 212.4.96.23
ns4.gnet.es. 3 A 212.4.96.24
ns5.gnet.es. 3 A 212.4.96.23
ns6.gnet.es. 3 A 35.180.217.196
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0