Apex domains cannot have CNAME records.
Question and response
Question
dig sub192.55.136.210.in-addr.arpa. NS
Answer
sub192.55.136.210.in-addr.arpa. 5 NS ns.jp.betrend.com.
sub192.55.136.210.in-addr.arpa. 5 NS ns.betrend.com.
Authority
The response has no authority records.
Additional
ns.jp.betrend.com. 5 A 210.153.89.42
ns.betrend.com. 5 A 52.197.195.60
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0