AdMob ads not working in Android Build Unity 2017.4.3f1

I've been trying for days to figure out how to implement admob ads into a unity project with little to no luck and it has become infuriating. the code below is a (verbatim) copy of the Admob getting started video here: https://youtu.be/UOptam261Ts

(The AdUnitId's are the provided by google Id's for running test ads.) GoogleMobileAdsDemoScript.cs :

 using UnityEngine;
 using GoogleMobileAds;
 using GoogleMobileAds.Api;
 using System;
 
 public class GoogleMobileAdsDemoScript : MonoBehaviour {
 
     private RewardBasedVideoAd rewardBasedVideoAd;
 
     public void Start() {
         rewardBasedVideoAd = RewardBasedVideoAd.Instance;
 
         // Called when an ad request has successfully loaded.
         rewardBasedVideoAd.OnAdLoaded += HandleRewardBasedVideoLoaded;
         // Called when an ad request failed to load.
         rewardBasedVideoAd.OnAdFailedToLoad += HandleRewardBasedVideoFailedToLoad;
         // Called when an ad is shown.
         rewardBasedVideoAd.OnAdOpening += HandleRewardBasedVideoOpened;
         // Called when the ad starts to play.
         rewardBasedVideoAd.OnAdStarted += HandleRewardBasedVideoStarted;
         // Called when the user should be rewarded for watching a video.
         rewardBasedVideoAd.OnAdRewarded += HandleRewardBasedVideoRewarded;
         // Called when the ad is closed.
         rewardBasedVideoAd.OnAdClosed += HandleRewardBasedVideoClosed;
         // Called when the ad click caused the user to leave the application.
         rewardBasedVideoAd.OnAdLeavingApplication += HandleRewardBasedVideoLeftApplication;
     }
 
     public void OnGUI()
     {
         GUIStyle style = new GUIStyle();
 
         Rect rect = new Rect(0, 0, Screen.width, Screen.height);
         style.alignment = TextAnchor.LowerRight;
         style.fontSize = (int)(Screen.height * 0.06f);
         style.normal.textColor = new Color(0f, 0f, .5f, 1f);
 
         GUI.skin.button.fontSize = (int)(0.035f * Screen.width);
         float buttonWidth = 0.35f * Screen.width;
         float buttonHeight = 0.15f * Screen.height;
         float columnOnePosition = 0.1f * Screen.width;
 
         Rect requestRewardRect = new Rect(columnOnePosition, 0.1f * Screen.height, buttonWidth, buttonHeight);
 
         Rect showRewardRect = new Rect(columnOnePosition, 0.3f * Screen.height, buttonWidth, buttonHeight);
 
         if (GUI.Button(requestRewardRect, "Request\nRewarded Video"))
         {
             LoadRewardBasedAd();
         }
 
         if (GUI.Button(showRewardRect, "Show\nRewarded Video"))
         {
             ShowRewardBasedAd();
         }
     }
 
     private void LoadRewardBasedAd() {
 #if UNITY_EDITOR
         string adUnitId = "unused";
 #elif UNITY_ANDROID
         string adUnitId = "ca-app-pub-3940256099942544/7325402514";
 #endif
         rewardBasedVideoAd.LoadAd(new AdRequest.Builder().Build(), adUnitId);
     }
 
     void ShowRewardBasedAd()
     {
         if (rewardBasedVideoAd.IsLoaded())
         {
             rewardBasedVideoAd.Show();
         }
         else print("Ad not ready!");
     }
 
 
     public void HandleRewardBasedVideoLoaded(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleRewardBasedVideoLoaded event received");
     }
 
     public void HandleRewardBasedVideoFailedToLoad(object sender, AdFailedToLoadEventArgs args)
     {
         MonoBehaviour.print(
             "HandleRewardBasedVideoFailedToLoad event received with message: "
                              + args.Message);
     }
 
     public void HandleRewardBasedVideoOpened(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleRewardBasedVideoOpened event received");
     }
 
     public void HandleRewardBasedVideoStarted(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleRewardBasedVideoStarted event received");
     }
 
     public void HandleRewardBasedVideoClosed(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleRewardBasedVideoClosed event received");
     }
 
     public void HandleRewardBasedVideoRewarded(object sender, Reward args)
     {
         string type = args.Type;
         double amount = args.Amount;
         MonoBehaviour.print(
             "HandleRewardBasedVideoRewarded event received for "
                         + amount.ToString() + " " + type);
     }
 
     public void HandleRewardBasedVideoLeftApplication(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleRewardBasedVideoLeftApplication event received");
     }
 }

Additionally, I have:

• downloaded the most recent package from their GitHub repo

• force-resolved Android dependencies and updated the version via unity menu options.

• Updated my version of Unity ( to 2017.4.3f1 )

• Run my Android in development build

• Tried implementing other ad types such as banner.

• Run my Android Build in ADB Logcat

When ran in adb using Adb Logcat -s Unity in the console, I get this error message though, as if the ad continuously fails to load and instead throws a timeout error. (I've tried many times to get it to work in the case that it could just be a timeout error, but no luck )

  HandleRewardBasedVideoFailedToLoad event received with message: Internal error
 06-29 16:14:50.664 31067 31067 I Unity   : UnityEngine.DebugLogHandler:Internal_Log(LogType, String, Object)
 06-29 16:14:50.664 31067 31067 I Unity   : UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
 06-29 16:14:50.664 31067 31067 I Unity   : UnityEngine.Logger:Log(LogType, Object)
 06-29 16:14:50.664 31067 31067 I Unity   : UnityEngine.Debug:Log(Object)
 06-29 16:14:50.664 31067 31067 I Unity   : UnityEngine.MonoBehaviour:print(Object)
 06-29 16:14:50.664 31067 31067 I Unity   : GoogleMobileAdsDemoScript:HandleRewardBasedVideoFailedToLoad(Object, AdFailedToLoadEventArgs) (at C:\

Does anyone have an idea of what I must be doing wrong here? any guidance would be greatly appreciated!

Also, if anyone is wondering about the scene, It is a simple scene with only a main camera and the GoogleMobileAdsDemoScript.cs attached as a component.