You must have both an ABN and and ATF to be on the GoFundraise platform.
You must at least have an authority to fundraise in the state that you are based as an organisation. Please note that you may also need an Authority to Fundraise (ATF) if you are holding your event in another state.
It's important that you contact your local authority to check your specific requirements.
The ATF is different from an ABN (an Australian Business Number), which is a unique identifier. This is issued by the Australian Business Register which is operated by the Australian Taxation Office.
For more information, please find: http://www.abn.business.gov.au/Faq.aspx