Hi,
I went to check on your website but I don't see any price nor add to cart button on your website so I can't look at your checkout.
First, I would recommend to only leave the Australia Post shipping method activated and disable the others.
That way, on the checkout, you should have an error message telling you why it can't display shipping rates from Australia Post.
And make sure that when you do your tests, you have a valid address in your shipping address.
And make sure that your products have a weight and dimensions.