The GSP is delivered to Australia by FedEx who can not deliver to a PO box.

Sometimes they hand smaller parcels on the Australia Post for delivery.

Ebay will not answer your email.....I doubt that they would have the faintest idea how the system works in practice.

You do not receive any notification of intended delivery.   All you will get is a notice if there was a delivery attempt made and no-one was there.   FedEx will make 2 delivery attempts before you have to pick up from their depot and you will be told where you have to pick up from.