Apex domains cannot have CNAME records.
Question and response
Question
dig fnz.co.uk. NS
Answer
fnz.co.uk. 5 NS unicorn.fnzc.co.uk.
fnz.co.uk. 5 NS robin.fnz.net.
fnz.co.uk. 5 NS lion.fnz.net.
Authority
The response has no authority records.
Additional
lion.fnz.net. 5 A 185.65.130.132
robin.fnz.net. 5 A 185.65.128.132
unicorn.fnzc.co.uk. 5 A 82.113.134.174
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0