I went online and the tracking site can’t find the tracking number, or it does not work - why is that??

For the US Postal Service - one of four reasons, number one, they have not updated the website, number two, no post office employee has manually scanned the package yet, or they have actually processed it without scanning because maybe they could not get it to scan and would not take the time to manually key in the number, or four, Internationally the package is NOT trackable as SMALL Flat Rate Priority mail packages and International Flat Rate letters are NOT trackable.