Sound works in the browser but not nativ on android!

Hi Folks,
I’m new here.
Ionic is a great framework and I really enjoy it.
One thing deosn’t work for me, and I tried a lot of workarounds, unfortunately still not resolved.
NativeAudio play’s sounds in the test environment(browser) very well.
After creating debug file for android , copy package on the device , executing, no sound audible?
Any Idea??
My Code:
Service:
import { Injectable } from ‘@angular/core’;
import { Platform } from ‘ionic-angular’;
import { NativeAudio } from ‘@ionic-native/native-audio’;

/*
Generated class for the SmartAudioProvider provider.

See https://angular.io/guide/dependency-injection for more info on providers
and Angular DI.
*/
@Injectable()
export class SmartAudio {

audioType: string = ‘html5’;
sounds: any = [];

constructor(public nativeAudio: NativeAudio, platform: Platform) {

  if(platform.is('cordova')){
      this.audioType = 'native';
  }

  if(platform.is('android')){
    this.audioType = 'native';
}

}

preload(key, asset) {

  if(this.audioType === 'html5'){

      let audio = {
          key: key,
          asset: asset,
          type: 'html5'
      };

      this.sounds.push(audio);

  } else {

      //this.nativeAudio.preloadSimple(key, asset);
      this.nativeAudio.preloadComplex(key, asset,1,1,0).then(onSuccess=>{

      let audio = {
          key: key,
          //asset: key,
          asset: asset,
          type: 'native'
      };

      this.sounds.push(audio);
  },onError=>{} );
}      

}

onSuccess()
{

}

play(key){

  let audio = this.sounds.find((sound) => {
      return sound.key === key;
  });

  if(audio.type === 'html5'){

      let audioAsset = new Audio(audio.asset);
      audioAsset.play();

  } else {

/*
this.nativeAudio.play(audio.asset).then((res) => {
console.log(res);
}, (err) => {
console.log(err);
});
*/

     this.nativeAudio.play(audio.key).then((res) => {
        console.log(res);
    }, (err) => {
        console.log(err);
    });

  }

}

}

App:
//app.component
initializeApp() {
this.platform.ready().then(() => {
// Okay, so the platform is ready and our plugins are available.
// Here you can do any higher level native things you might need.
this.statusBar.styleDefault();
this.splashScreen.hide();
this.smartAudio.preload(‘horn’, ‘assets/sounds/horn.mp3’);

  this.smartAudio.preload('error', 'assets/sounds/Fehler.wav');
  this.smartAudio.preload('ok', 'assets/sounds/Gut.wav');
  
});

in page:
playAudio(found:boolean) {

if ( found )
this.smartAudio.play(‘ok’);
else
this.smartAudio.play(‘error’);

}

Thesounds files are stored in /assets/sounds