I suspect the brightly coloured cap and surface texture of the cap count against it being an Agaricus. It might be a slightly immature fruit body of a Laccaria but the surface texture of the cap doesn't seem right.
Thanks KenT - i just chose that because it was at the top of the list (and you cant choose 'unknown') - it didnt to me look like any of the funghi in the image library on the app.
I can see why KenT thought of Laccaria (but with doubts). I won't make any other guess. Since the ACT is likely to have several hundred easily seen (but not necessarily easily identified) fungi it will take some time for the image library to include them.
Michael, I apologize for being unclear. When I said that I wouldn't make any other guess I should have said that I agreed with KenT's doubts and wouldn't dare make any suggestion at all. For now, this immature mushroom is still a puzzle to me.