What's this all about?
When you start the game, Modrinth App passes a special key called “access token” to it. This key is then used to call Minecraft authentication servers to “assign” your account to a particular server when you join one, in order to verify your ownership of the game and authenticity of the account.
If this key becomes stale, for example, as a result of having the game open for too long, or a bug in the app, trying to join a server will result in an “Invalid session (Try restarting your game and the launcher)” error.
Just restart your game
Most of the time, just restarting your game is enough. Modrinth App should refresh your token if it's expired the moment you start the game. You can also restart the app, just to be extra sure that the token is refreshed.
Sign out and sign back in
Sometimes, restarting the app and the game may not work, and you will keep getting the same error. This is definitely an issue with the app that we're looking to fix in the future updates.
However, you can work around that by simply signing out of your Minecraft account in the app, and then signing back in. This will ensure that the app creates a new token. Well, sometimes at least… see below.
Deleting Minecraft authorizations file
It seems that due to a bug in Modrinth App 0.7.0 and above, the app will sometimes refuse to refresh your token completely, even after you sign out and sign back in. We're currently investigating how and why this happens.
As a workaround to that, you can do the following:
Open ⚙️ Settings in Modrinth App.
Copy the current path to App directory.
Open the copied path in file explorer.
Close the app.
In the app's directory, go to the
caches→metadatafolder.In the
metadatafolder delete theminecraft_auth.jsonfile.Restart the app.
Try to sign in and join multiplayer server again.
Deleting minecraft_auth.json completely deletes any Minecraft authorization data that the app has stored.
What?! This didn't work either?
Maybe the app isn't to blame, and it happens that the Minecraft authentication servers are down. Although if that that happens, the newest versions of the game should tell you that instead of telling that your session is invalid.
You can check the official @MojangStatus Twitter account for the status updates of the publicly acknowledged accidents, or Downdetector website, to see if other users have any issues as well. Lastly, you can also verify that this is not Modrinth App for sure, by opening the game in the official Minecraft Launcher and trying to connect to a server.
If this actually happens to be the accident on Mojang's side, there's not much we can do about it. You will have to wait until Mojang engineers fix the servers. Remember that accidents like this can happen to anyone, so be patient :)