Apex domains cannot have CNAME records.
Question and response
Question
dig plusvps.com. NS
Answer
plusvps.com. 2 NS ns3.phg.hr.
plusvps.com. 2 NS ns2.phg.hr.
plusvps.com. 2 NS ns1.phg.hr.
Authority
The response has no authority records.
Additional
ns1.phg.hr. 2 A 212.44.101.101
ns2.phg.hr. 2 A 178.218.162.218
ns3.phg.hr. 2 A 5.144.175.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0