Unity ads working in Editor, but not working in Android

I’ve made a simple endless runner game, and used Unity ads in it. On testing in the editor, the ads work showing the unity ad images, but when i build the apk and install on android, no ads work. Neither the banner nor the interstitial. Please help.
This is the script I’m using to initialize the ads.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Advertisements;
public class AdScript : MonoBehaviour
{
string gameId = “*******”;
bool testMode = true;
public string placementId = “bannerad”;
public string interstid = “LevelComplete”;
private static AdScript inst = null;
public static AdScript Inst
{
get { return inst; }
}
void Awake()
{
if (inst != null && inst != this)
{
Destroy(this.gameObject);
return;
}
else
{
inst = this;
}
DontDestroyOnLoad(this.gameObject);
}
void Start()
{
Advertisement.Initialize(gameId, testMode);
StartCoroutine(ShowBannerWhenInitialized());
Debug.Log(“Initialized ads”);
}
public void ShowInterstitialAd()
{
if (Advertisement.IsReady())
{
Advertisement.Show(interstid);
}
else
{
Debug.Log(“Interstitial ad not ready at the moment! Please try again later!”);
}
}
IEnumerator ShowBannerWhenInitialized()
{
while (!Advertisement.isInitialized)
{
yield return new WaitForSeconds(0.5f);
}
Advertisement.Banner.SetPosition(BannerPosition.TOP_LEFT);
Advertisement.Banner.Show(placementId);
}
}

I don’t see any obvious errors in your code so it should be working. Do you see any errors appear in Logcat?

(You can see Logcat output from within the Unity Editor using this package: Android Logcat Guide | Package Manager UI website)