What exactly doesn't work? Please be specific.

I have the multiplayer campaign button available under campaign and I can see the overview of available servers hosting a campaign.

When I host a game myself I can see a button in the lobby "Script Disclaimer" with the following info:

"Due to a lack of networking functionality in Total War:
Attila's scripting environment, a great number of scripted features have been disabled for multiplayer campaigns.

Enabled Features:
- Invasions
- Papal Favour
- Starting Battles
- War Weariness
- World Events

Partially Working Features:
- Dynamic Faction Names (Automatic)
- Kingdom Events (Automatic)
- Story Events (HRE & Sicily Disabled)

Disabled Features:
- Annexing Vassals
- Buffer States
- Challenges
- Crusades
- Decisions
- Holy Roman Empire System
- Ironman/Achievements
- Population"

There could be some typo's above, since I typed everything from a screenshot as copy pasting wasn't possible.