captcha in unity3d

using UnityEngine;

namespace avstn.captcha
{
    public delegate void CaptchaHandler();

    public class Captcha : MonoBehaviour
    {
        public int lengthCode;

        public string dictWord;
        public char dictSeparator;

        private int indexSymb = 0;

        private int countError = 0;

        private bool isDisplay = false;

        private string[] dictionary;

        private string[] captchaCode;

        public Texture bgImage;
        public Texture borderSymbImg;

        public Rect rBgImage;

        public Vector2 symbOffs;
        public Vector2 symbSize;

        public GUIStyle styleSymb;

        public event CaptchaHandler notifySuccess;
        public event CaptchaHandler notifyError;

        private const int MAX_ERROR_INPUT = 2;

        private void Awake()
        {
            dictionary = dictWord.Split(dictSeparator);

            if (lengthCode == 0)
                lengthCode = 5;
        }

        private void OnGUI()
        {
            if (isDisplay)
            {
                displayCaptcha();
                keyDownSymb();
            }
        }

        public void run(int length)
        {
            captchaCode = createCode(length, dictionary);

            isDisplay = true;
        }

        private void displayCaptcha()
        {
            GUI.DrawTexture(rBgImage, bgImage);

            for (int i = 0; i < captchaCode.Length; i++)
                GUI.Box(new Rect(new Vector2( symbOffs.x + (i * symbSize.x), symbOffs.y ), symbSize), captchaCode[i], styleSymb);

            GUI.DrawTexture(new Rect( new Vector2( symbOffs.x + (indexSymb * symbSize.x), symbOffs.y ), symbSize ), borderSymbImg);
        }

        private string[] createCode(int length, string[] dictionary)
        {
            string[] code = new string[length];

            for (int i = 0; i < length; i++)
                code[i] = dictionary[Random.Range(0, dictionary.Length - 1)];

            return code;
        }

        private void keyDownSymb()
        {
            Event ev = Event.current;

            if (ev.type == EventType.KeyDown)
            {
                KeyCode key = ev.keyCode;

                if (key != KeyCode.None)
                {
                    if (key.ToString() == captchaCode[indexSymb])
                    {
                        indexSymb++;

                        if (indexSymb >= lengthCode)
                        {
                            reset();

                            if (notifySuccess != null)
                                notifySuccess();
                        }
                    }
                    else
                    {
                        countError++;

                        if (countError >= MAX_ERROR_INPUT)
                        {
                            reset();

                            if (notifyError != null)
                                notifyError();
                        }
                    }
                }
            }
        }

        private void reset()
        {
            indexSymb = 0;
            countError = 0;
            isDisplay = false;
        }
    }
}

// example of work and how to connect to your game https://youtu.be/5I46ngrCX3k
// my parametrs in inspector https://imgur.com/a/dF3YEAb