Apex domains cannot have CNAME records.
Question and response
Question
dig digimobil.es. NS
Answer
digimobil.es. 5 NS ns.rdsnet.org.
digimobil.es. 5 NS ns.rdsnet.tech.
digimobil.es. 5 NS ns.rdsnet.eu.
digimobil.es. 5 NS ns.rdsnet.ro.
Authority
The response has no authority records.
Additional
ns.rdsnet.eu. 4 A 82.79.10.12
ns.rdsnet.ro. 4 A 79.118.155.12
ns.rdsnet.org. 4 A 86.121.222.12
ns.rdsnet.tech. 4 A 188.27.120.12
ns.rdsnet.eu. 4 AAAA 2a02:2f09:3100:0:0:0:0:a
ns.rdsnet.ro. 4 AAAA 2a02:2f01:100:0:0:0:0:a
ns.rdsnet.org. 4 AAAA 2a03:9c20:1000:0:0:0:0:a
ns.rdsnet.tech. 4 AAAA 2a03:9c20:f000:0:0:0:0:a
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0