Errors "Failed to login - null" or "Failed to login - invalid session" when joining a server

Issue description

These errors mostly happen when there is a Microsoft account autentication issue on your Launcher, whether it is Technic or CurseForge. 

Solution

Closing the game and launcher completely, logging out from the launcher and relogging back would be the most common fixes, but if that still doesn't work, you can access '%appdata%/roaming/.technic' and delete the 'oauth' folder.

If this still doesn't solve it, you can open a support ticket on our Discord server.