Apex domains cannot have CNAME records.
Question and response
Question
dig ppoiss.ee. NS
Answer
ppoiss.ee. 5 NS ns3.radicenter.ee.
ppoiss.ee. 5 NS ns4.radicenter.fi.
ppoiss.ee. 5 NS ns1.radicenter.com.
ppoiss.ee. 5 NS ns2.radicenter.eu.
Authority
The response has no authority records.
Additional
ns1.radicenter.com. 5 A 185.86.211.11
ns2.radicenter.eu. 5 A 94.237.27.189
ns3.radicenter.ee. 5 A 90.191.43.167
ns4.radicenter.fi. 5 A 94.237.119.73
ns1.radicenter.com. 5 AAAA 2a13:c5c0:dc1:0:0:0:0:11
ns2.radicenter.eu. 5 AAAA 2a04:3542:1000:910:34cf:d8ff:fe6d:6dbb
ns3.radicenter.ee. 5 AAAA 2001:7d0:5341:ce00:0:0:0:1
ns4.radicenter.fi. 5 AAAA 2a04:3540:1000:310:34cf:d8ff:fe6d:5bc1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0