Apex domains cannot have CNAME records.
Question and response
Question
dig ip-51-83-3.eu. NS
Answer
ip-51-83-3.eu. 4 NS ns113.ovh.net.
ip-51-83-3.eu. 4 NS dns113.ovh.net.
Authority
The response has no authority records.
Additional
ns113.ovh.net. 2 A 5.135.82.125
dns113.ovh.net. 2 A 5.196.46.145
ns113.ovh.net. 2 AAAA 2001:41d0:b01:100:0:0:0:2
dns113.ovh.net. 2 AAAA 2001:41d0:d01:700:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0