Just curious about eBay virtual tracking number, this is the explanation from eBay
For sellers who are using an Australia Post product, eBay’s Virtual Tracking Number has got you covered. This is an alphanumeric code ('ebay' + 7 characters) that ensures we receive accurate tracking information and gives your buyers more visibility on the delivery of their items. Remember to not remove or interfere with the code on your orders to ensure we get your tracking.
If eBay generated the shipping label for an order, they must already know the Australia Post tracking number.
If seller took it to Australia Post and updated the tracking number for an order, they are also linked.
So, what is the use of eBay's virtual tracking number? An order can already link to Australia Post without another ID.
No idea what it does, but its the line eBay adds to the label above the address, looks like
ebay:z123abcd
123 Street Road
Town place NSW 2000