Unfortunately I can't verify if Serbia is in the list since the URL doesn't load for me as I'm in a restricted country.I am from serbia
It does not seem like, Serbia is on the list. That being said I dont think, I have even seen a player from Serbia on ACR Poker. I have also never seen "error code 500", so no idea what it means. Maybe OP could try to uninstall the poker client/App and then install again?Have you verified that you're not in a banned jurisdiction by ACR? They made some changes a while ago and blacklisted more countries: