Hi @dinoflint. Thanks for being part of GoDaddy Community! In a situation like this, a customer care agent should be able to tell you why the registration has been failing. Unfortunately, since this isn't a support forum, no one here would be able to give you more information. You can also check out this article which explains the requirements for .com.au domain registrations. Hope that helps.
JesseW - GoDaddy | Community Manager | 24/7 support available at x.co/247support | Remember to choose a solution and give kudos.