FacebookAds\Api::init("XXX", "YYY", "ZZZ");
$api = FacebookAds\Api::instance();

$form = new FacebookAds\Object\LeadgenForm(1234);

$fields = [
	FacebookAds\Object\Fields\LeadFields::AD_ID,
	FacebookAds\Object\Fields\LeadFields::AD_NAME,
	FacebookAds\Object\Fields\LeadFields::ADSET_ID,
	FacebookAds\Object\Fields\LeadFields::ADSET_NAME,
	FacebookAds\Object\Fields\LeadFields::FIELD_DATA,
	FacebookAds\Object\Fields\LeadFields::CREATED_TIME,
];

foreach ($facebook->getLeads($fields) as $lead) {
  // $lead->getData()['adset_name'] is always empty
}