Apex domains cannot have CNAME records.
Question and response
Question
dig 8.36.189.in-addr.arpa. NS
Answer
8.36.189.in-addr.arpa. 5 NS ns1.scaladatacenters.com.
8.36.189.in-addr.arpa. 5 NS ns2.scaladatacenters.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0