Admob Banner Not Working! Getting Crazy With This!

Hi there!

I got a game released on the Play Store but I'm not being able to set up a banner correctly.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using GoogleMobileAds.Api;
5. public class GoogleMobileAdsDemoScript : MonoBehaviour
6. {
7.     private BannerView bannerView;
8.     public void Start()
9.     {
10. #if UNITY_ANDROID
11.         string appId = "ca-app-pub-XXX";
12. #elif UNITY_IPHONE
13.             string appId = "ca-app-pub-XXX";
14. #else
15.             string appId = "ca-app-pub-XXX";
16. #endif
17.         // Initialize the Google Mobile Ads SDK.
18.         MobileAds.Initialize(appId);
19.         this.RequestBanner();
20.     }
21.     private void RequestBanner()
22.     {
23. #if UNITY_ANDROID
24.         string adUnitId = "ca-app-pub-XXX";
25. #elif UNITY_IPHONE
26.             string adUnitId = "ca-app-pub-XXX";
27. #else
28.             string adUnitId = "ca-app-pub-XXX";
29. #endif
30.         // Create a 320x50 banner at the top of the screen.
31.    
32.         bannerView = new BannerView(adUnitId, AdSize.Banner, AdPosition.Bottom);
33.         AdRequest request = new AdRequest.Builder().Build();
34.         bannerView.LoadAd(request);
35.     }
36. }

This is my code, is exactly the same as the Tutorial on the main website, and it's attached to the main camera. I don't see anything in the Unity Editor or Android device...
I need help please!