Scene loading not working, how to fix it?

Question

C++ / C#

The code doesn't work. Where did you make a mistake? He does not write problems, there are 2d colliders. Nothing happens on click

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

public class LoadScene : MonoBehavior
{

public int N;

public void OnMouseDown ()
{

SceneManager.LoadScene(N);

}

}

Answer 1

Didn't work through ui images, did the same, but through regular ones and everything went well

Answer 2

Well, I'm 100% sure that no one has read the docs, but why is this needed, of course. File - Build Settings and there it will add a scene to Unity