Apex domains cannot have CNAME records.
Question and response
Question
dig ip-57-131-4.eu. NS
Answer
ip-57-131-4.eu. 5 NS dns19.ovh.net.
ip-57-131-4.eu. 5 NS ns19.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0