Apex domains cannot have CNAME records.
Question and response
Question
dig 192.146.89.in-addr.arpa. NS
Answer
192.146.89.in-addr.arpa. 5 NS b.inet.ns01.eu.
192.146.89.in-addr.arpa. 5 NS d.inet.ns01.eu.
192.146.89.in-addr.arpa. 5 NS a.inet.ns01.eu.
192.146.89.in-addr.arpa. 5 NS c.inet.ns01.eu.
Authority
The response has no authority records.
Additional
a.inet.ns01.eu. 5 A 217.160.80.161
b.inet.ns01.eu. 5 A 217.160.81.161
c.inet.ns01.eu. 5 A 185.132.35.161
d.inet.ns01.eu. 5 A 185.132.34.161
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0