Then what has Australian GST got to do with the purchase if neither the buyer nor the seller are in Australia?

It is now January 2021 and I am currently trying to get a GST refund from eBay after receiving a refund from an overseas seller (item did not arrive)
You would think by now they have implemented an automatic refund process but instead they try to convince you that the ATO needs to refund you and i need to contact them. Matter is now escalated after i mention the ACCC.

If the seller had refunded through the paypal transaction then the GST would have been refunded automatically.

If the refund was sent to you as a payment to you then it is not automatic....paypal does not know that it was a transaction involving GST.