When a company conducts a pre-IPO, they are unlikely to issue a full disclosure document which is why the new shares are only offered to investors eligible under s708 of the Corporations Act 2001(Cth). Companies typically only open pre-IPOs to sophisticated and professional investors, but sometimes they are also made available to experienced investors.
The requirements for each classification of investor as required under s708 of the Corporations Act 2001(Cth) can be found here.
You may apply via OnMarket to qualify your investment profile(s). More information can be found here or via the Investment Profiles section of your OnMarket Dashboard.