Apex domains cannot have CNAME records.
Question and response
Question
dig domain.cam. NS
Answer
domain.cam. 1 NS ns2.domain.cam.
domain.cam. 1 NS ns1.domain.cam.
Authority
The response has no authority records.
Additional
ns1.domain.cam. 1 A 91.208.175.102
ns2.domain.cam. 1 A 87.255.57.102
ns1.domain.cam. 1 AAAA 2a00:ddc0:1:1:0:0:0:102
ns2.domain.cam. 1 AAAA 2a00:ec8:400:ff10:0:0:0:103
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0