Facebook app invite for android

Question

I am working on a new android app and I want to integrate the 'Invite Friends' from fb in order to invite them to use the app. I have added the required code in the app, I've also created the app in the developer portal from Facebook, but users are not getting the notification if I share it. I tried to also add the user in the settings -> tester users and yet no notification for them. Can someone help me on this? I over searched the internet, but I could find an answer on this.

Code used for opening the sharing dialog:

    private void InviteFriends()
    {
        if (AppInviteDialog.CanShow())
        {
            var content = new AppInviteContent.Builder()
                              .SetApplinkUrl(Resources.GetString(Resource.String.app_url))
                        //.SetPreviewImageUrl(previewImageUrl)
                        .Build();
            AppInviteDialog.Show(this, (AppInviteContent)content);
        }
    }

Thank you in advance, Alex