Invalid channel for service notification error even after creating custom channel

I've implemented a startForeground() method to start the ongoing notification which is called in onCreate(). There are two usages in two different classes. I'm testing on API 27 (Android 8.1)

First Usage (PictureCapturingService.java):

onCreate():

@Override
public void onCreate() {
    super.onCreate();
    Context mContext = this.getApplicationContext();
    context = this.getApplicationContext();

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        startMyOwnForeground();
    } else {
        startForeground(1234, new Builder(getApplicationContext()).setContentTitle("Capturing Image").setContentText("").setSmallIcon(R.drawable.icon_notif).build());
    }

startMyOwnForeground():

@RequiresApi(api = Build.VERSION_CODES.O)
private void startMyOwnForeground() {
    String channelID = "com.example.code";
    NotificationChannel notificationChannel = new NotificationChannel(channelID, "Background Service", NotificationManager.IMPORTANCE_NONE);
    notificationChannel.enableLights(false);
    notificationChannel.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
    NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    assert manager != null;
    manager.createNotificationChannel(notificationChannel);

    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this, channelID);
    Notification notification = notificationBuilder.setOngoing(true)
            .setSmallIcon(R.drawable.icon_notif)
            .setContentTitle("Capturing Image")
            .setPriority(NotificationManager.IMPORTANCE_MIN)
            .setCategory(Notification.CATEGORY_SERVICE)
            .build();

    startForeground(1234, notification);
}

Second Usage (VideoRecordService.java):

Gets called from onCreate() and startRecord()

onCreate():

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        startMyOwnForeground("Sending Message");
    }
    else {
        startForeground(1234, new Builder(this).setContentTitle("Sending Message").setContentText("").setSmallIcon(R.drawable.icon_notif).build());
    }

startRecord():

private void startRecord() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        startMyOwnForeground("Video Recording");
    } else {
        startForeground(1234, new Builder(getApplicationContext()).setContentTitle("Video Recording").setContentText("").setSmallIcon(R.drawable.icon_notif).build());
    }

startMyOwnForeground:

@RequiresApi(api = Build.VERSION_CODES.O)
private void startMyOwnForeground(String str) {
    String channelID = "com.example.code";
    NotificationChannel notificationChannel = new NotificationChannel(channelID, "Background Service", NotificationManager.IMPORTANCE_NONE);
    notificationChannel.enableLights(false);
    notificationChannel.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
    NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    assert manager != null;
    manager.createNotificationChannel(notificationChannel);

    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this, channelID);
    Notification notification = notificationBuilder.setOngoing(true)
            .setSmallIcon(R.drawable.icon_notif)
            .setContentTitle(str)
            .setPriority(NotificationManager.IMPORTANCE_MIN)
            .setCategory(Notification.CATEGORY_SERVICE)
            .build();

    startForeground(1234, notification);
}

I receive the following error:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.raudram.barathikannamma, PID: 18871
android.app.RemoteServiceException: Bad notification for startForeground: java.lang.RuntimeException: invalid channel for service notification: Notification(channel=null pri=0 contentView=null vibrate=null sound=null defaults=0x0 flags=0x40 color=0x00000000 vis=PRIVATE)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1797)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:176)
    at android.app.ActivityThread.main(ActivityThread.java:6651)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824)

Your icon is set to R.mipmap.ic_launcher. By name, that suggests that you are trying to use your app launcher icon as your notification icon. That is not a valid notification icon, though.

Use the Image Asset Wizard in Android Studio to create a dedicated notification icon — you will find a dedicated "Notification Icons" category for the "Icon Type" in the wizard. Then, switch to using that resource, instead of R.mipmap.ic_launcher, and see if you have better results.