@Vantari Somi Custom commands which support voice assistants feature of Azure speech service is not available in Australia East region currently. The list of supported regions are listed here. If you can create a resource in one of the supported regions this page should load as expected.
The message that is displayed is not very intuitive, I will pass this feedback to our team so it could be fixed in future releases.
Please feel free to accept this response as answer if it helps. Thanks.