Apex domains cannot have CNAME records.
Question and response
Question
dig 0-15.243.254.194.in-addr.arpa. NS
Answer
0-15.243.254.194.in-addr.arpa. 5 NS ns4.partage.renater.fr.
0-15.243.254.194.in-addr.arpa. 5 NS dns01.partage.renater.fr.
0-15.243.254.194.in-addr.arpa. 5 NS dns02.partage.renater.fr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0