Apex domains cannot have CNAME records.
Question and response
Question
dig xtra.co.nz. NS
Answer
xtra.co.nz. 3 NS ns-838.awsdns-40.net.
xtra.co.nz. 3 NS ns-1109.awsdns-10.org.
xtra.co.nz. 3 NS ns-1689.awsdns-19.co.uk.
xtra.co.nz. 3 NS ns-297.awsdns-37.com.
Authority
The response has no authority records.
Additional
ns-297.awsdns-37.com. 2 A 205.251.193.41
ns-838.awsdns-40.net. 2 A 205.251.195.70
ns-1109.awsdns-10.org. 2 A 205.251.196.85
ns-1689.awsdns-19.co.uk. 2 A 205.251.198.153
ns-297.awsdns-37.com. 2 AAAA 2600:9000:5301:2900:0:0:0:1
ns-838.awsdns-40.net. 2 AAAA 2600:9000:5303:4600:0:0:0:1
ns-1109.awsdns-10.org. 2 AAAA 2600:9000:5304:5500:0:0:0:1
ns-1689.awsdns-19.co.uk. 2 AAAA 2600:9000:5306:9900:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0