XML-RPC metaWeblog.newPost . How to manage enclosures ?

Hi,
Does anybody knows how to manage enclosures with metaWeblog.newPost method https://codex.www.ads-software.com/XML-RPC_MetaWeblog_API.

I take a look at the method implementation in : wp-includes/class-wp-xmlrpc-server.php and saw those interesting lines :

// Handle enclosures
		...
		if ( is_array( $enclosure ) && isset( $enclosure['url'] ) && isset( $enclosure['length'] ) && isset( $enclosure['type'] ) ) {

Does any body know how to manage enclosure with this method ?
I tried this but definitevly doesn’t work, post is remotely created but not with enclosure :

$content = array(
            'title' => 'title',
            'description' => 'description',
            'mt_allow_comments' => 0,  // 1 to allow comments
            'mt_allow_pings' => 0,  // 1 to allow trackbacks
            'post_type' => 'post',
            'mt_keywords' => '',
            'categories' => array(''),
			'enclosure' => array('url'=>'https://www.education.gov.yk.ca/pdf/pdf-test.pdf','length'=>'','type' =>'')
);

$params = array(0,'admin','admin',$content,false);

if (!$client->query('metaWeblog.newPost',$params))
{
	echo('Error occured while executing method : ' . $client->getErrorCode().":".$client->getErrorMessage());
}

$response = $client->getResponse();
var_dump($response) ;

Greetings,
ben