Apex domains cannot have CNAME records.
Question and response
Question
dig 128-255.94.71.206.in-addr.arpa. NS
Answer
128-255.94.71.206.in-addr.arpa. 4 NS ns-1059.awsdns-04.org.
128-255.94.71.206.in-addr.arpa. 4 NS ns-212.awsdns-26.com.
128-255.94.71.206.in-addr.arpa. 4 NS ns-732.awsdns-27.net.
128-255.94.71.206.in-addr.arpa. 4 NS ns-1958.awsdns-52.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0