A recommendation is not an instruction or warning.
This missing invoice situation must be lost in translation surely. What invoice would I have that I can provide? I sent a package, I didn’t provide any service I can show an invoice for
Did you provide customs information?
All international shipments require what Nik is referring to as an "invoice". I'm not sure what AUS requires, but I'm sure you have to fill out some form for exporting goods. It's not a matter of a service being performed, but a declaration page.
I'm not sure this is really Nik's problem. You shipped the piece. He isn't responsible for something out of his control when he already recommended something. Your going to have to contact whoever is holding your package to figure out what is needed.