I think that many people have such a problem.

When asking with a stack overflow, there was an answer "It will be displayed if payment information is completed". But now we can not set payment information unless we earn more than 8000 yen($100).

Since I was able to display test advertisements, I think these problems are not a problem of Unity or SDK. I think it is a problem within AdMob.

There were other answers. The respondent said that "AdMob's advertisement unit will be displayed as time passes after it was made." However, two weeks have passed since I made an ad unit!

Every answer was not what I was looking for.
When I was investigating other questions, I often found that the common answer is "Do you mistake AppID and adUnitID?"
I confirmed it over and over but there was no mistake.

There are no errors in the Unity Console.

I set personal information on the AdMob console.
I also set up payment service.

I do not know what to do. Please tell me.

Script↓

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using GoogleMobileAds.Api;

public class GoogleMobileAdsDemoScript : MonoBehaviour

 private BannerView bannerView;

 public void Start()
 
 this.RequestBanner();
 

 private void RequestBanner()
 
#if UNITY_ANDROID
 string adUnitId = "My UnitID";
#elif UNITY_IPHONE
 string adUnitId = "My Ad Unit ID";
#else
 string adUnitId = "unexpected_platform";
#endif

 bannerView = new BannerView(adUnitId, AdSize.SmartBanner, AdPosition.Bottom);

 AdRequest request = new AdRequest.Builder().Build();

 bannerView.LoadAd(request);
 

I am convinced that adUnitID is not mistaken.
When I changed adUnitID to the following string, test advertisement was displayed.

ca-app-pub-3940256099942544/6300978111

But when I made this string my own ad unit ID, the ad did not show up.

AndroidManifest.xml↓

<?xml version="1.0" encoding="utf-8"?>
<!--
This Google Mobile Ads plugin library manifest will get merged with your
application's manifest, adding the necessary activity and permissions
required for displaying ads.
-->
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
 package="com.google.unity.ads"
 android:versionName="1.0"
 android:versionCode="1">
 <uses-sdk android:minSdkVersion="14"
 android:targetSdkVersion="19" />
 <application>
 <!-- Sample AdMob App ID: ca-app-pub-XXXXXXXXXXXXXXXX~XXXXXXXXXX -->
 <meta-data
 android:name="com.google.android.gms.ads.APPLICATION_ID"
 android:value="My APP ID"/>
 </application>
</manifest>

I think that this script and xml file are not involved in this issue, what do you think?

(Although it may not be necessary) Additional information↓

・SDK platforms → Android 8.1, Android 7.1.1, Android 6.0

・Google Play Services → installed (version 49)

・CMake → installed

・NDK → installed

・Support Repository → installed all

You cannot set bank information until you earn your first $100.
However you can and need to set all the other financial information and personal information. Once you have done this, it will display ads. Usually within a few hours.

Go to -> Payments
In payments, the bottom left section should contain an option to change settings.

This will open up a screen where you can add/ edit a payment profile. This is what is required.