Uncaught Error: missing serializer: at getSerializer (Serializer.ts:23:30) at Room.onMessageCallback (Room.ts:228:36)

[GitOutOfMyBed]

I'm not sure what the problem is. I have simplified my code down significantly yet I am still getting errors:
I'm new to Colyseus and am building a Phaser/Colyseus web game. I have been stuck on this bug here:

Uncaught Error: missing serializer: 
    at getSerializer (Serializer.ts:23:30)
    at Room.onMessageCallback (Room.ts:228:36)
getSerializer @ Serializer.ts:23
onMessageCallback @ Room.ts:228

I'm not sure what the issue is. I've cut down my code significantly to this:

This is my backend server GameRoom.ts file:

import { Room } from "colyseus";
import { Schema, type } from "@colyseus/schema";

class GameRoomState extends Schema {
  @type("number") score: number = 0;
}

export default class GameRoom extends Room {
  state = new GameRoomState();

  onCreate(options) {}
}

And this is my client Phaser Game.js file:

class GameScene extends window.Phaser.Scene {
  client = new window.Colyseus.Client("ws://localhost:2567");
  room;

  constructor() {
    super();
  }

  preload() {
    this.load.image("bg", "images/background3.png");
  }

  async create() {
    try {
      const connection = this.client.joinOrCreate("game_room");

      this.room = await connection;
    } catch (e) {
      console.error("Failed to connect to Colyseus server:", e);
    }
  }

  update() {}
}

const config = {
  type: window.Phaser.AUTO,
  width: window.innerWidth,
  height: window.innerHeight,
  scene: GameScene,
  physics: {
    default: "arcade",
    arcade: {
      debug: false,
    },
  },
  scale: {
    mode: window.Phaser.Scale.RESIZE,
  },
};

const game = new window.Phaser.Game(config);

```I also have additional package.json, tsconfig.json, index.html, and index.js server files but I don't think the problem is coming from them. According to the tutorials this is all I need but I am still getting this error.

[endel]

This error is likely due to mixture of 0.15 and 0.16 versions between server and client. These versions are not compatible with each other.