Check the group before sharing a code

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For a normal player-hosted session, compare the group's platforms with this table compiled from the publisher's support FAQ. A Game ID does not remove platform restrictions. Publisher multiplayer FAQ

GroupCompatibility check
Steam, GOG, Epic Games Store or Microsoft Store on PCEnable cross-play in gameplay settings when mixing PC storefronts
PlayStation 4 and PlayStation 5The publisher supports play within the PlayStation family
Xbox One and Xbox Series X or SThe publisher supports play within the Xbox family
PC and a consoleThe publisher does not support this combination

The FAQ lists up to eight players for PC, PlayStation and Xbox, and four for Nintendo Switch. These are player-hosted limits, not a promise about custom dedicated-server configurations. Common Questions distinguishes ordinary hosting from running a separate server.

Join the host's current world

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The host enters a world with a character, opens the pause menu with Escape on PC, and uses Copy game ID. Send that code privately. The joining player selects Join Game, pastes it into Enter Game ID, and joins. Use a freshly copied code when checking a failed attempt. Publisher joining instructions

Work through a failed connection

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This is a diagnostic order, not a claim that each check fixes every network error. Change one condition at a time and record the result.

CheckEvidence to collect before the next attempt
Group matches the compatibility tableEach player's platform and PC storefront
Everyone is using the same releaseThe displayed game versions, after checking for updates
The host is in the intended worldConfirmation from the host, followed by a freshly copied Game ID
Mixed PC storefronts have cross-play enabledThe gameplay setting checked by each player
The failure can be repeatedThe exact message, who hosted, who joined and when the error appeared

Checking versions has a documented reason: the publisher's earlier stability notes fixed a session-ending problem involving an outdated client joining a newer host. The notes also describe fixes for hidden network errors and interrupted cross-play sessions. They are historical bug fixes, not evidence that a current failure has the same cause. Post-launch stability notes, pages 1 and 6-7

Send a useful bug report

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If the checklist does not isolate the problem, report the exact sequence rather than only "multiplayer is broken." Include the platform/storefront list, versions, host and joining roles, full error message, and whether the same pair can connect with their roles reversed. Keep Game IDs and personal account information out of public screenshots.

The publisher links its bug-report form from the Core Keeper support page. For a new group's first expedition after connecting, use Tips for Beginners and agree which characters and world to use before gathering resources.