Apex domains cannot have CNAME records.
Question and response
Question
dig finvoicer.fi. NS
Answer
finvoicer.fi. 4 NS ns3.euronic.fi.
finvoicer.fi. 4 NS ns1.euronic.fi.
finvoicer.fi. 4 NS ns2.euronic.fi.
Authority
The response has no authority records.
Additional
ns1.euronic.fi. 4 A 185.55.84.18
ns2.euronic.fi. 4 A 185.55.84.19
ns3.euronic.fi. 4 A 92.243.21.222
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0