I made test project to get player object in client but it doesn't work

ARR

this is my whole code of my test project

but it return null when I use GetPlayerObject() on client

what did I miss?

    private NetworkRunner runner;

    [SerializeField]
    private GameObject playerObj;

    private void Start()
    {
        runner = gameObject.AddComponent<NetworkRunner>();
        runner.ProvideInput = true;
    }

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.F1))
        {
            Debug.LogError("Host");

            var args = new StartGameArgs();
            args.SessionName = "a";
            args.GameMode = GameMode.Host;
            args.SceneManager = gameObject.AddComponent<NetworkSceneManagerDefault>();

            runner.StartGame(args);
        }

        if (Input.GetKeyDown(KeyCode.F2))
        {
            Debug.LogError("Client");

            var args = new StartGameArgs();
            args.SessionName = "a";
            args.GameMode = GameMode.Client;

            runner.StartGame(args);
        }

        if (Input.GetKeyDown(KeyCode.F3))
        {
            Debug.LogError("ShutDown");

            runner.Shutdown();
        }

        if (Input.GetKeyDown(KeyCode.F4))
        {
            foreach (var player in runner.ActivePlayers)
            {
                runner.SetPlayerObject(player, runner.GetPlayerObject(player));
                Debug.LogError($"{player}, {runner.GetPlayerObject(player)}");
            }
        }

        if (Input.GetKeyDown(KeyCode.F5))
        {
            foreach (var player in runner.ActivePlayers)
            {
                Debug.LogError($"{player}, {runner.GetPlayerObject(player)}");
            }
        }
    }

    public void OnPlayerJoined(NetworkRunner runner, PlayerRef player)
    {
        var obj = runner.Spawn(playerObj, new Vector3(UnityEngine.Random.Range(-5f, 5f), 0, 0), null, player);
        runner.SetPlayerObject(player, obj);
        Debug.LogError($"{player}, {runner.GetPlayerObject(player)}");
    }