I have a question for the Terminal Hacker project (Udemy Unity Course)

[Samuel_Morris]

I previously asked this question, but the topic was closed and marked as answered before I could get clarification on an answer.
Here’s the original question:

I am using Unity 2019.3.13f1 and the Archived Complete C# Unity Game Developer 3D course on Udemy. Since I am using the Archived course, I can’t use the Q&A.

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I've got an error in Unity,

I’m not sure how to fix this problem. Could someone help me?
(Original question end)

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The answer I got told me to check the lines of code the error referred to and to check the Lecture’s Project Changes. I did both of these, to no avail. I saw no differences between my code and the Project Changes, but something may have slipped my notice. Here’s my code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Hacker : MonoBehaviour
{

    // Game config. Data
    string[] level1Passwords = {"connection", "router", "watch", "play", "stream", "load" };
    string[] level2Passwords = { "Masterpiece", "Borrow", "recive", "Checkout", "script", "character" };

    //Game State
    int level;
    enum Screen { MainMenu, Password, Win };
    Screen currentScreen;
    string password;

    // Start is called before the first frame update
    void Start()
    {

        ShowMainMenu();
    }

    void ShowMainMenu()
    {
        Screen currentScreen = Screen.MainMenu;
        Terminal.ClearScreen();
        Terminal.WriteLine("What would you like to hack into?");
        Terminal.WriteLine("Press 1 for the WIFI");
        Terminal.WriteLine("Press 2 for the Library");
        Terminal.WriteLine("Selection: ");
    }

    void OnUserInput(string input)
    {
        if (input == "menu")
        {
            ShowMainMenu();
        }
            else if (currentScreen == Screen.MainMenu)
        {
            RunMainMenu(input);

        }
        else if (currentScreen == Screen.Password)
        {
            CheckPassword(input);

        }
    }

    void RunMainMenu(string input)
    {
            bool isValidLevelNumber = (input == "1" || input == "2");
        if (isValidLevelNumber)
        {
            level = int.Parse(input);
            StartGame();
        }
        else if (input == "pogchamp")
        {
            Terminal.WriteLine("You're my little pogchamp");
        }
        else
        {
            Terminal.WriteLine("Please choose a valid level");
        }


    }

        void StartGame(int level)
        {
            currentScreen = Screen.Password;
            Terminal.ClearScreen();
            Terminal.WriteLine("Please enter your Password: ");
        }
        
        void CheckPassword(string input)
        {
            if (input == password)
            {
                Terminal.WriteLine("Access Granted");
            }
            else
            {
                Terminal.WriteLine("Wrong! Try again...");
            }
        }
    }

Could someone please help me?

[codermonk]

void RunMainMenu(string input)
    {
            bool isValidLevelNumber = (input == "1" || input == "2");
        if (isValidLevelNumber)
        {
            level = int.Parse(input);
            StartGame();  // No parameter passed to StartGame...
        }

The error appears at the line StartGame(); above:
Try changing

 level = int.Parse(input);
StartGame();

 level = int.Parse(input);
StartGame(level); // passing the variable 'level' to the StartGame function