Apex domains cannot have CNAME records.
Question and response
Question
dig im. NS
Answer
im. 5 NS barney.advsys.co.uk.
im. 5 NS hoppy.iom.com.
im. 5 NS ns4.ja.net.
im. 5 NS pebbles.iom.com.
Authority
The response has no authority records.
Additional
ns4.ja.net. 5 A 193.62.157.66
hoppy.iom.com. 5 A 217.23.163.140
barney.advsys.co.uk. 5 A 217.23.160.50
pebbles.iom.com. 5 A 83.218.14.53
ns4.ja.net. 5 AAAA 2001:630:0:47:0:0:0:42
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0