ok so if Aus post accept the online payment as proof would they accept that if the parcel was lost and could I then make a claim through Aus post for items up to $50, or is there no such thing as claiming through the post office.

Officially, there is no compensation for lost C&S parcels unless the extra $1 for signature on delivery has been paid. The AP rep that posts here (Alice), has stated that if, upon investigation, the loss is found to be due to AP's negligence, then compensation would be paid, but if all you have is proof of online payment and no tracking events, it would probably be difficult to determine where/how the loss occurred and I doubt Australia Post would take responsibility.

With signature on delivery, compensation up to $100 may be paid.