$requests = function($audience) use ($client, $activity, $profile, $payload, $userAgent) {
            foreach($audience as $url) {
                $headers = HttpSignature::sign($profile, $url, $activity, [
                    'Content-Type'    => 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"',
                    'User-Agent'    => $userAgent,