Is the discord link expired? Or is it bugged?
Viewing post in Early Access 0.4.3.3 is now Available! comments
Neither, it must be on your side, check if your ip isn't banned/ shadow banned by dicsord, if you aren't trying to join the server while being in 100 other servers, etc. just Google or use ai for troubleshooting, all I can say is that the discord invite link works
(Try this one instead https://discord.gg/recgame)