Apex domains cannot have CNAME records.
Question and response
Question
dig ddns.com.au. NS
Answer
ddns.com.au. 4 NS dns1.quick.net.au.
ddns.com.au. 4 NS dns4.quick.net.au.
ddns.com.au. 4 NS dns3.quick.net.au.
ddns.com.au. 4 NS dns2.quick.net.au.
Authority
The response has no authority records.
Additional
dns1.quick.net.au. 4 A 49.255.194.121
dns2.quick.net.au. 4 A 175.45.125.28
dns3.quick.net.au. 4 A 172.104.39.245
dns4.quick.net.au. 4 A 45.33.13.58
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0