Apex domains cannot have CNAME records.
Question and response
Question
dig 0-26.169.51.209.in-addr.arpa. NS
Answer
0-26.169.51.209.in-addr.arpa. 5 NS dns2.planisys.net.
0-26.169.51.209.in-addr.arpa. 5 NS dns1.planisys.net.
0-26.169.51.209.in-addr.arpa. 5 NS dns3.planisys.net.
Authority
The response has no authority records.
Additional
dns1.planisys.net. 5 A 131.108.40.7
dns2.planisys.net. 5 A 179.63.251.216
dns3.planisys.net. 5 A 190.185.104.7
dns1.planisys.net. 5 AAAA 2803:bc00:0:0:0:0:0:84
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0