Foreground service returns a Notification Error based on Channel ID on API 29, and not on API 26. How to retrieve proper Channel ID?

I get the following error when running this Service on my smartphone (API 29) but not in another one (API26). For the error I assume that the problem is with the Channel ID when running my service as a ForegroundService, but I coulnd't find out how to solve it... I didn't know which Channel Id would be the appropiate. Any help?

Error:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.android.testworkmanager, PID: 22582
    android.app.RemoteServiceException: Bad notification for startForeground: java.lang.RuntimeException: invalid channel for service notification: Notification(channel=TestChannelID pri=2 contentView=null vibrate=null sound=null tick defaults=0x0 flags=0x40 color=0x00000000 vis=PRIVATE)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1969)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:224)
        at android.app.ActivityThread.main(ActivityThread.java:7520)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
E/MQSEventManagerDelegate: failed to get MQSService.

This is my manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.android.testworkmanager">

    <uses-permission android:name="android.permission.FOREGROUND_SERVICE"/>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <service
            android:name=".MyService"
            android:enabled="true"
            android:exported="false"
            android:icon="@drawable/ic_launcher_background"
            android:label="MyServiceLabel" />

        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

and this is my service:

package com.example.android.testworkmanager;

import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;

import androidx.core.app.NotificationCompat;


public class MyService extends Service {
    private static final int ONGOING_NOTIFICATION_ID = 2;
    private String channelID = "TestChannelID";

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        //TODO do something useful
        Log.v("APP_TEST","Service_startCommand");


        Intent notificationIntent = new Intent(this, MyService.class);
        PendingIntent pendingIntent =
                PendingIntent.getActivity(this, 0, notificationIntent, 0);


        Notification notification =
                new NotificationCompat.Builder(this, this.channelID)
                        .setContentTitle("TestNotification")
                        .setContentText("This is the text to display on notification")
                        .setSmallIcon(R.drawable.ic_launcher_background)
                        .setContentIntent(pendingIntent)
                        .setTicker("TickerText")
                        .setPriority(NotificationCompat.PRIORITY_MAX)
                        .build();

        startForeground(ONGOING_NOTIFICATION_ID, notification);

        return Service.START_STICKY;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.v("APP_TEST","Service_Create");
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.v("APP_TEST","Service_destroy");
    }

    @Override
    public IBinder onBind(Intent intent) {
        //TODO for communication return IBinder implementation
        return null;
    }
}

And the service would be started and stopped with the following commands:

//For starting
        Intent intent = new Intent(this, MyService.class);
        startService(intent);

... (somewhere else)

//For stopping
        Intent intent = new Intent(this, MyService.class);
        stopService(intent);

For starting a foreground service in Android O and above, you have to create a channel, before you create a notification. And you also have to put the same channel id in your Notification.Builder constructor. Here is an example on how to create a channel:

/**
 * Method that create a channel for notification showed to user, for foreground service
 */
@RequiresApi(api = Build.VERSION_CODES.O)
private void createChannel() {
    NotificationManager nm = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

    NotificationChannel mChannel = new NotificationChannel(CHANNEL_ID,
            CHANNEL_NAME,  //name of the channel
            NotificationManager.IMPORTANCE_HIGH);   //importance level

    // Configure the notification channel.
    mChannel.setDescription("Description of your channel");
    mChannel.enableLights(true);

    // Sets the notification light color for notifications posted to this channel, if the device supports this feature.
    mChannel.setShowBadge(true);
    assert nm != null;
    nm.createNotificationChannel(mChannel);
}