How to add 'Admod's ads without exception?

Question

I'm setting up an Admon's ad to my activity in my Android app. But When I did all instructions , still get IllegalStateException.

I searched for stackoverflow and Googled it. Here is the links : Unable to get provider com.google.android.gms.ads.MobileAdsInitProvider: java.lang.IllegalStateException: Why? React native Admob Unable to get provider com.google.android.gms.ads.MobileAdsInitProvider: java.lang.IllegalStateException: . By the way I have tried implementation com.google.firebase:firebase-ads:15.0.1. But It worked on emulator but not real device. And I cannot see my ad on real device working. So that I am using implementation 'com.google.android.gms:play-services-ads:17.1.1'. I did google docs what did it say :

Totally my xml :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="">
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"></uses-permission>
    <supports-screens
        android:anyDensity="true"
        android:largeScreens="true"
        android:normalScreens="true"
        android:resizeable="true"
        android:smallScreens="true" />
    <meta-data
        android:name="com.google.android.gms.ads.AD_MANAGER_APP"
        android:value="true"/>
    <meta-data
        android:name="com.google.android.gms.ads.APPLICATION_ID"
        android:value="ca-app-pub-8855622609935813xxxxxxxxx"/>
 <application
 android:allowBackup="true"
        android:icon="@drawable/logom"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
   <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".start" />
        <activity android:name=".end_of_start" />
        <activity android:name=".end_of_fail" />
        <activity android:name=".last_level" />
        <activity android:name=".tutorial"></activity>
    </application>
</manifest>

My layout' s adview :

<com.google.android.gms.ads.AdView xmlns:ads="http://schemas.android.com/apk/res-auto"
        android:id="@+id/adView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        ads:adSize="BANNER"
        ads:adUnitId="ca-app-pub-8855622609935813xxxxxxx">
 </com.google.android.gms.ads.AdView>

MainActivity :

 mAdView = findViewById(R.id.adView);
     MobileAds.initialize(this, "ca-app-pub-8855622609935813xxxxxx");
   AdView adView = new AdView(this);
 adView.setAdSize(AdSize.BANNER);
   adView.setAdUnitId("ca-app-pub-8855622609935813xxxxxxx");
  AdRequest adRequest = new AdRequest.Builder().build();
        mAdView.loadAd(adRequest); 

Lastly my gradle:app's library : implementation 'com.google.android.gms:play-services-ads:17.1.1'

I want to work my app with Admob's ad. After that; I set my app to google play for other customers using.