Route to Greece

toothpick johnny:
The normal green card will cover you for EU countries only so if you want to transit Croatia and or Serbia you will have to add it on or pay at the border crossing.

This is not true, my Polish green card was covering me in all countries except Iraq, Afghanistan and some African countries. The same is written on my British one, except that it’s valid for up to three months only. So I do not understand why your green card is worse than mine…