change to id

convex/world.ts

@@ -193,7 +193,7 @@ export const leaveWorld = mutation({
     await insertInput(ctx, world._id, 'leave', {
       playerId: existingPlayer.id,
     });
-    world.players.delete(oauthToken);
+    world.players.delete(existingPlayer.id);
   },
 });