Test-Multiplayer/Assets/Scripts/Chat/LoginUI.cs

using UnityEngine;
using UnityEngine.UI;
using Mirror;
using TMPro;

public class LoginUI : MonoBehaviour
{
    [Header("UI Elements")]
    [SerializeField] internal TMP_InputField usernameInput;
    [SerializeField] internal Button clientButton;
    [SerializeField] internal Text errorText;

    public static LoginUI instance;

    string originalNetworkAddress;

    void Awake()
    {
        instance = this;        
    }

    void Start() 
    {
        if (string.IsNullOrWhiteSpace(NetworkManager.singleton.networkAddress))
            NetworkManager.singleton.networkAddress = "localhost";

        originalNetworkAddress = NetworkManager.singleton.networkAddress;
    }

    void Update()
    {
        if (string.IsNullOrWhiteSpace(NetworkManager.singleton.networkAddress))
            NetworkManager.singleton.networkAddress = originalNetworkAddress;
    }

    public void ToggleButton(string username)
    {
        clientButton.interactable = !string.IsNullOrWhiteSpace(username);
    }

    public void OnClientButton()
    {
        var username = usernameInput.text.Trim();

        Debug.Log($"[LoginUI] Client button pressed. Username length: {username.Length}");

        if (string.IsNullOrWhiteSpace(username))
        {
            Debug.LogWarning("[LoginUI] Client start blocked because the username is empty.");
            if (errorText != null) { errorText.text = "Enter a username"; errorText.gameObject.SetActive(true); }
            return;
        }

        // set the name on the ChatAuthenticator (if present)
        var auth = NetworkManager.singleton.GetComponent<ChatAuthenticator>();
        if (auth != null)
        {
            Debug.Log("[LoginUI] Assigning username to ChatAuthenticator.");
            auth.SetPlayerName(username);
        }
        else
            Debug.LogWarning("LoginUI: ChatAuthenticator not found on NetworkManager.");

        // start client
        Debug.Log($"[LoginUI] Starting client. Network address: '{NetworkManager.singleton.networkAddress}'");
        NetworkManager.singleton.StartClient();
    }
}