Frustation over unity ads To Display Ad

Hello everybody! hope you all doing good.

So recenlty I started working with ads. However, I can't really get them to work. I just want a simple BOX/IMAGE WITH COLLIDER OR 2D SPRITE when you touch it, an AD will display. That's all. however it's not working. My game is android and this is my script. Does the OnMouseDown not work with android touch? and when I tried it. It does work, however it's very buggy (sometimes it works, sometimes not and then it stops working) What I have here is a simple box collider and this script. Thanks guys!

 using UnityEngine;
 using System.Collections;
 using UnityEngine.Advertisements;
 
 
 public class Touch2 : MonoBehaviour {
     
     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
         void OnMouseDown() {
             //now your gameObject was clicked!
             Advertisement.Initialize ("57898");
             if(Advertisement.isReady()){ Advertisement.Show(); }
         }
     }