Ionic com admob-free ad displays only " Nice Job"

I created an application with Ionic version: 3.20.1 and configured with admobfree:

cordova plugin add cordova-plugin-admob-free --save --variable ADMOB_APP_ID="ca-app-pub-XXXXXXXXXXXXXXXX/XXXXXXXXXX"

ionic cordova plugin add cordova-plugin-admob-free --save --variable ADMOB_APP_ID="ca-app-pub-XXXXXXXXXXXXXXXX/XXXXXXXXXX"

It is already included in config.xml

<plugin name="cordova-plugin-admob-free" spec="0.25.0">
    <variable name="ADMOB_APP_ID" value="ca-app-pub-XXXXXXXXXXXXXXXX/XXXXXXXXXX" />
</plugin>

And in my TS are with all the requested settings:

import { Component } from '@angular/core';
import { NavController, Platform } from 'ionic-angular';
import { BarcodeScanner, BarcodeScannerOptions, BarcodeScanResult } from '@ionic-native/barcode-scanner';
import { ScanResultPage } from '../scan-result/scan-result';
import { AdMobFree, AdMobFreeBannerConfig } from '@ionic-native/admob-free';

@Component({
  selector: 'page-home',
  templateUrl: 'home.html'
})
export class HomePage {

  constructor(
    private platform:Platform,
    public navCtrl: NavController,
    private barcodeScanner: BarcodeScanner,
    private admobFree: AdMobFree) {

    let bannerConfig: AdMobFreeBannerConfig = {
      autoShow: true,
     id : 'ca-app-pub-XXXXXXXXXXXXXXXX/XXXXXXXXXX'
    };
    this.admobFree.banner.config(bannerConfig);

    this.admobFree.banner.prepare().then(() => {
    }).catch(e => alert(e));
  }

The ad appears, but only shows the test ad:

Does anyone know how I can proceed ?

Updated: 02/03/2019

I tried to see with this plugin also, more unsuccessfully: Using Admob With Ionic Framework