How to put ads in your game

Hello,
I'm sorry for posting this, since there is, probably a lot of these posts, but I haven't been able to find one that helps. I am using a simple code to implement ads in my game, but its not working.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.SceneManagement;
5. using UnityEngine.Advertisements;
6.  
7. public class LevelMenu : MonoBehaviour
8. {
9.     public void Menu()
10.     {
11.         SceneManager.LoadScene("Menu");
12.     }
13.  
14.     public void DisplayAd()
15.     {
16.         if (Advertisement.IsReady())
17.         {
18.             Advertisement.Show();
19.         }
20.     }
21. }
22.  

I have ads enabled in the editor and I have test mode on. The two functions in the code both connect to a button. When I press the button, no ads show up, so I'm wondering why. I've tried to display the ad by just pressing "K" to see if it was a problem with the button, but it still didn't work...

[EDIT] I got it working. I needed to switch the platform to Android.