Apex domains cannot have CNAME records.
Question and response
Question
dig 26.4.62.in-addr.arpa. NS
Answer
26.4.62.in-addr.arpa. 5 NS nsb.online.net.
26.4.62.in-addr.arpa. 5 NS nsa.online.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0