Multiplayer not working? Check these first
Platform combination
PC and consoles, or PlayStation and Switch, cannot play together.
Match the game version
Make sure both the host and the joining player are on the latest version.
Game ID and settings
Paste the Game ID again. For PC players on different stores, the host must set the multiplayer connection setting to all PC players.
Multiplayer errors: causes and fixes by message
| Message (summary) | Cause | Fix |
|---|---|---|
| “Crossplay is not supported, so your platform is not compatible with the host” | The two platforms cannot play together (PC with console, PlayStation with Switch, etc.). | Play on platforms from the same family (combinations). |
| “The host does not allow crossplay” | The host has blocked PC players from other stores. | The host sets the multiplayer connection setting to all PC players. |
| “There seems to be a problem with crossplay” | The connection between different stores is not working. | The game suggests that the host turning crossplay off in the game settings may help (players from the same store don’t need crossplay). |
| “Game version mismatch” | The host and the joining player are on different game versions. | Update both to the latest version. On Steam, check for updates in your library and make sure you have not opted into a beta. |
| “The session supports up to N players and is currently full” | The host’s session is at its player limit. | Wait for someone to leave (how many players). |
| “The host is not ready yet” | The host has not finished loading into the world. | Try joining again once the host is in the world. |
| “Connection timed out / Connection failed / Failed after several retries” | The network cannot connect, or the Game ID is wrong. | Paste the Game ID again, ask the host to refresh the ID, and check both internet connections. |
| “Lost connection to the multiplayer backend” | The connection to the multiplayer service dropped. | As the message suggests, leave the world and open it again. |
| “Could not start a multiplayer session; check your internet connection” | A console could not start multiplayer. | Check your internet connection and the status of your platform’s online service (PS Plus, etc.). |
| “A required mod is missing on the server” | The host and the joining player have different mods installed. | Install the same mods or remove them (how to install mods). |
Messages are summarized in plain English; the exact in-game wording may differ.
What to check when multiplayer fails without a message
- Check the platform combination: only PC with PC, PS4 with PS5, Xbox One with Xbox Series, and Switch with Switch 2 can play together.
- Update both games: right after an update is released, it is common for one side to still be on the old version.
- Make a new Game ID: the host refreshes the password and Game ID from the pause menu and sends the new ID (this does not affect progress).
- Reopen the world: the host leaves the world and opens it again.
- Remove mods: if you use mods on PC, try again without them.
The basic steps are in how to play multiplayer.
More on platforms and multiplayer
Unless a note on the page says otherwise, numbers are read from the game files of Core Keeper 1.3.0.6 (prefabs, configuration files, drop tables and the game's program) and calculated by this site, including upgraded (per-level) values, sell prices and mana costs. Names and descriptions are the game's official English text. Only reinforcing materials, minion and pet attacks and some food values are based on the Core Keeper Wiki (Fandom) data (CC BY-SA 3.0). Core Keeper and its images are © Pugstorm. This is an unofficial fan site.