'application/json', 'X-CUSTOM-HEADER' => 'my-custom-header', ]; $multi_curl = new MultiCurl(); $multi_curl->beforeSend(function ($instance) use ($headers) { foreach ($headers as $key => $value) { $instance->setHeader($key, $value); } }); $multi_curl->addGet('https://www.example.com/'); $multi_curl->addGet('https://www.example.org/'); $multi_curl->addGet('https://www.example.net/'); $multi_curl->start();