How to get online multiplayer working again

How to fix currently broken online skirmish mode.

Why is it broken?

Battletech uses a deprecated chat filter service. It stopped working in 2022 and since then you can't create an online lobby.

How to fix?

There'a an official mod that fixes the issue:
https://forum.paradoxplaza.com/forum/threads/important-if-you-want-to-play-multiplayer-read-this-post.1560206/

In short:
1. Launch the game and make sure the mods are enabled: Main menu -> Mods -> Mods enabled chekbox
2. Exit game
3. Download this archive https://drive.google.com/file/d/1os1uX87nVBlY9zOckUU1Ig7oQN8LnBTM/view?usp=share_link
4. Extract it into C:\Users\{user_name}\Documents\My Games\BattleTech\mods​\BtMpFix
5. Launch the game again. Now you should have BattleTech Multiplayer Fix in your mods list

Hosting a lobby

If you are hosting a lobby, and players trying to join get an error: "Server failed to respond in time", or as a host you see players connecting and immediately disconnecting, you have to open port 11001 on your router or add it to your firewall rule. If you don't know how to forward a port on your router, try this guide: https://www.wikihow.com/Set-Up-Port-Forwarding-on-a-Router