composer require league/flysystem-dropboxVisit https://www.dropbox.com/developers/apps and get your "App secret".
You can also generate OAuth access token for testing using the Dropbox App Console without going through the authorization flow.
use League\Flysystem\Dropbox\DropboxAdapter;
use League\Flysystem\Filesystem;
use Dropbox\Client;
$client = new Client($accessToken, $appSecret);
$adapter = new DropboxAdapter($client, [$prefix]);
$filesystem = new Filesystem($adapter);