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Can't join the server — error breakdown

Outdated client and Outdated server, Failed to verify username and Invalid session, Connection refused and timed out, Unknown host, mod mismatch — what the player and the server owner should do.

Updated October 24, 2026

Look at the error text on the disconnect screen — it almost always names the cause. For each error below, first comes what the player can do, then what the server owner should check.

The easiest way to join without version errors

Join the server from the launcher: in the servers section, find the server by name or address in the “Server name or address” field and click “Play”. The launcher will pick the right version and join the server itself.

Outdated client / Outdated server

“Outdated client” means the game version is older than the server's. “Outdated server” is the opposite — the game is newer than the server.

For the player: find out the server version and change the modpack version: modpack → “Settings” → “Version and loader” → “Change”. If the modpack has mods, it's safer to create a separate modpack for that version with the “New modpack” button.

For the owner: the versions must match, or install ViaVersion — Outdated client and Outdated server, Joining from different versions.

Failed to verify username / Invalid session

“Invalid session” or Failed to verify username means the server verifies the Minecraft license, and the login failed the check.

For the player:

  • If you play by nickname (offline account) or with a Millida account, you can't join a server with license verification — you need a Microsoft account with the game purchased. For account types, see the article Minecraft license and login.
  • If you have a Microsoft account but it says “Log in again” under the nickname, your session has expired. Click the account, confirm the login and restart the game.

For the owner: to allow players without a license — Nickname login and Failed to verify username: server setup.

Connection refused

The server didn't accept the connection: it's off, asleep, still starting, or the address points somewhere else.

For the player: check the address and wait a couple of minutes. If other players can't join either, the server is off — message the owner.

For the owner: Connection refused: troubleshooting. On the free plan, a player joining doesn't wake a sleeping server — it's started from the control panel.

Connection timed out

There's no response from the server. Most often the address has a typo or the player's network is blocking the connection: the provider, a VPN, mobile internet.

For the player: double-check the address, turn off the VPN, try another network — for example, tethering from your phone. If other servers won't open either, the problem is your internet.

For the owner: Connection timed out.

Unknown host

The address couldn't be found: it has a typo or the domain isn't working yet.

For the player: check the address letter by letter — no spaces and no http://. The port is written after a colon: play.example.net:25566. If the address is correct, restart your router or change the DNS in your network settings.

For the owner: your own domain doesn't start working immediately, it can take up to several hours — Your own domain.

Mod list mismatch

You can only join a modded server with a modpack that has the same mods of the same versions. The errors look like Mod rejections, Incompatible FML modded server, Mismatched mod channel list, or a disconnect right after joining.

For the player: ask the owner for the server modpack. If the modpack is in the catalog or someone shared a code — install it: “Import” → “By code”. Don't build your own modpack for the server by hand — one mod of a different version is enough to break it.

For the owner: give players the same modpack that's on the server — Installing a modpack, Mod conflicts: how to find them.

Other errors