almost 3 years ago - AndrewT - Direct link
We are aware of an issue where some customers can't login/stay signed in with their Paradox account which then results in being unable to play multiplayer. With the latest patch it solved it for a vast majority of players but sadly not everyone >
Rest assured we're investigating this further and both the CKIII and tech team are trying to figure out the cause (and a solution!) but sadly there isn't a confirmed workaround for the time being :(. We have two possible workarounds that may solve it:

Disable IPv6
- Close CK3
- Go to Control Panel > View Network status and tasks > Change adapter settings (left side)
- Find your Hamachi Connection and Disable it
- Find your Internet connection adapter (for me, it was WiFi)
- Right click your internet adapter and select properties
- Scroll down to find "Internet Protocol Version 6 (TCP/IPv6) and uncheck the box
- Select Ok
- Start up CK3 and should work.

Use a VPN

- Obtain a VPN

- Set the country to the US (why this works is also an enigma ><)

- Start the game

- Sign in and see if it "sticks"