Backup storage in dropbox

I am doing work to keep backup of database and files in laravel 5.2 with laravel backup package (spatie) from this site

ERROR:

It was working when perfectly in local but It shows error when I changed this disk option to dropbox in config/laravel-backup.php as below

   'destination' => [

                /*
                 * The disk names on which the backups will be stored.
                 */
                'disks' => [
                    'dropbox',
                ],
            ],

I already created app and added dropbox in disk option in config/filesystems.php as below

'disks' => [

        'dropbox' => [
             'driver' => 'dropbox',
             'accessToken' => env('0jMXvhtOVgAAAAAAAAADCV1GsUJojer4Z5hyAsbYETDqS33tJAuhSC4_XHOE1X-s'),
             'appSecret' => env('sxwv5mhj6k52dg7'),
             'app' => 'Backup ghfnepal.org',
        ],

        'local' => [
            'driver' => 'local',
            'root' => storage_path('app'),
        ],

        'public' => [
            'driver' => 'local',
            'root' => storage_path('app/public'),
            'visibility' => 'public',
        ],

        's3' => [
            'driver' => 's3',
            'key' => 'your-key',
            'secret' => 'your-secret',
            'region' => 'your-region',
            'bucket' => 'your-bucket',
        ],

    ],

I already made DropboxFilesystemServiceProvider class and registered in provider option in config/app.php. While searching, I found this problem is common and went through many tutorials but couldn't solve.

via Chebli Mohamed