5008 - This means you are not on the latest build of the game and need to update it. Once you do so you should be good to go!
3201 - This means that you are unable to authenticate with the platform provider. This is occurring due to load on the servers and the requests timing out. While the error message says contact Support, there's no need, we get alerts from our monitoring systems. You can wait a bit and try, try again and should eventually get into the game. You can also check something like Downdetector to monitor your game platform health directly.
2001 - This means basically the same thing as 3201, however, you're likely authenticated with the platform and simply locked out of the game for the time being due to excessive server load and our need to throttle access to them. You can wait a bit and try, try again and should eventually get into the game.
5001, 5002- This means one of a few things: 1) That you tried joining a game session that is gone. Didn't refresh the war table for a long time and tried to join that game; 2) the game ended/closed before you tried joining on it. 3) that you joined on a friend who left that session and it closed up while they were joining in. It's a temporary issue and not something that is in need of a fix, just a retry on matchmaking.