Apex domains cannot have CNAME records.
Question and response
Question
dig gastuna.com. NS
Answer
gastuna.com. 5 NS ns3.gastuna.com.
gastuna.com. 5 NS ns2.gastuna.com.
gastuna.com. 5 NS ns1.gastuna.com.
Authority
The response has no authority records.
Additional
ns1.gastuna.com. 5 A 109.237.142.8
ns2.gastuna.com. 5 A 148.251.254.105
ns3.gastuna.com. 5 A 109.237.143.8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0