Orders suddenly having reference numbers above name in address

[ccrrefills]

In a few days, I had two orders, both from Australia, where the address above the recipient name has a line like:

Reference# ABN#0123456789 Code: PAID

What is this for? It often won't all fit on my shipping labels.

[pjcdn2005]

I believe that is ebays Australian tax number.  They are required to collect tax on items under $1000 sent to Australia’s so they are confirming on the label that the tax has been paid.