Question The type or namespace name 'IUnityAdsListener' could not be found (are you missing a using directive

Code (CSharp):

1. using System;
2. using UnityEngine;
3. using System.Collections;
4. using UnityEngine.Advertisements;
5.  
6. // Example script showing how to invoke the Google Mobile Ads Unity plugin.
7. public class Adcontrol : MonoBehaviour, IUnityAdsListener
8. {
9.     public bool forcoin;
10.     public static Adcontrol instace;
11.     public string GameId = "3988497";
12.     private bool testmode = false;
13.     public string videoAd = "video";
14.     public string banner = "banner";
15.     public string reward = "rewardedVideo";
16.     private void Awake()
17.     {
18.         instace = this;
19.     }
20.     // Start is called before the first frame update
21.     void Start()
22.     {
23.  
24.         Advertisement.Initialize(GameId, testmode);
25.  
26.         Advertisement.AddListener(this);
27.         showBanner();
28.  
29.  
30.     }
31.  
32.  
33.     public void showBanner()
34.     {
35.  
36.         StartCoroutine(ShowBannerWhenInitialized());
37.         Advertisement.Banner.SetPosition(BannerPosition.TOP_CENTER);
38.     }
39.  
40.     public void showAd()
41.     {
42.         if (!Advertisement.IsReady(videoAd)) { return; }
43.         Advertisement.Show();
44.     }
45.  
46.  
47.     IEnumerator ShowBannerWhenInitialized()
48.     {
49.         while (!Advertisement.isInitialized)
50.         {
51.             yield return new WaitForSeconds(0.5f);
52.         }
53.         Advertisement.Banner.Show(banner);
54.     }
55.  
56.     public void hideBanner()
57.     {
58.         Advertisement.Banner.Hide();
59.     }
60.  
61.  
62.     public void ShowRewardedVideo()
63.     {
64.         // Check if UnityAds ready before calling Show method:
65.         if (Advertisement.IsReady(reward))
66.         {
67.             Advertisement.Show(reward);
68.         }
69.         else
70.         {
71.             Debug.Log("Rewarded video is not ready at the moment! Please try again later!");
72.         }
73.     }
74.  
75.     // Implement IUnityAdsListener interface methods:
76.     public void OnUnityAdsDidFinish(string placementId, ShowResult showResult)
77.     {
78.         // Define conditional logic for each ad completion status:
79.         if (showResult == ShowResult.Finished)
80.         {
81.             AdManager.instance.give50points();
82.             AdManager.instance.forcoin = false;
83.            
84.             // Reward the user for watching the ad to completion.
85.             //  GameManager.instance.rewardUser();
86.         }
87.         else if (showResult == ShowResult.Skipped)
88.         {
89.             AdManager.instance.forcoin = false;
90.             // Do not reward the user for skipping the ad.
91.  
92.         }
93.         else if (showResult == ShowResult.Failed)
94.         {
95.             AdManager.instance.forcoin = false;
96.             Debug.LogWarning("The ad did not finish due to an error.");
97.         }
98.     }
99.  
100.     public void OnUnityAdsReady(string placementId)
101.     {
102.         // If the ready Placement is rewarded, show the ad:
103.         if (placementId == reward)
104.         {
105.             // Optional actions to take when the placement becomes ready(For example, enable the rewarded ads button)
106.         }
107.     }
108.  
109.     public void OnUnityAdsDidError(string message)
110.     {
111.         // Log the error.
112.     }
113.  
114.     public void OnUnityAdsDidStart(string placementId)
115.     {
116.         // Optional actions to take when the end-users triggers an ad.
117.     }
118.  
119.     // When the object that subscribes to ad events is destroyed, remove the listener:
120.     public void OnDestroy()
121.     {
122.         Advertisement.RemoveListener(this);
123.     }
124. }