Steam Multiplayer Most Important

Hi, everyone
I want to share one info about using Steam for Multiplayer free testing.
Most of you may know it, but i lost some time and nerves to find out about that problem.
Before joining the game, you must make a very important change in Steam Launcher Settings/Downloads. I attach a pic to be more clear.
Every player that want to join and play your game have to choose the same Region!
I hope that will help someone and save him a lot of troubles.

Regards and Best wishes.