@Richard1019 When I'm logged in as a host, I go to Insights, then Earnings. At the bottom of that page below my current-year earnings and stats, there are three links available:
View Transaction History
View Tax Information
Request Proof of Income (and says below, for refinancing your mortgage)
I'm in the US, but I can't imagine our interface is that different from yours. However, there could be some law or regulation in Australia that doesn't allow AirBnB to offer that option? Have you actually searched that page?