Why is the onclick method in unity not working?

Question

C++ / C#

why when I put this script on UI button in unity the onclick method doesn't see the "buy" function

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using UnityEngine.SceneManagement;
using System.IO;

public class shop : MonoBehaviour
{
    
    string datatext;

    public void buy(int numberofclick) 
    {
        datatext = File.ReadAllText("shopdata.txt");
        numberofclick = int.Parse(datatext);
        numberofclick = numberofclick * 2;
        File.WriteAllText("shopdata.txt", numberofclick.ToString());
        
        
    }
}

Answer 1

In OnClick, you need to add not the script itself, but the object on which this script is located.
Create a dummy in the hierarchy, drop the script there and add this dummy to the button

Answer 2

onclick may not work with the new inputmanager