It seems that the tracker does not detect the first phase of shipping (package accepted by origin facility) per the Post Serbia tracking system. Instead, the first recognized event is when the package is shipped to Post Serbia. This may be due to a null value in Phase for the package-accepted event.
Left is the official Post Serbia tracker at http://www.posta.rs/struktura/eng/aplikacije/alati/posiljke.asp and right is what is shown in the app.
This is not a huge problem, but it would be helpful to have the tracker start raising notifications earlier.
Thanks in advance!