eBay

I sold an item a day before ,ie 05/31 and today when I was ready to ship the itemI saw a note like this "eBay note: Ship by Friday, Jun 02" .Do you know what is all about ? It is the third time in a row that this happened to me.

I am from Greece and I sold an item to an Australian buyer by registered mail.The buyer messaged me that he has not received the item yet.When i try to track the item ,Australian Post Office returns this message - Sorry, this item can't be tracked -....