send email with google client php sdk

function send_email($subject, $body)
{
    $client = new Google_Client();
    $client->setAuthConfig('credentials.json');
    $client->addScope(Google_Service_Gmail::GMAIL_SEND);
    $client->setAccessType("offline");
    $client->setApprovalPrompt("force");

    $service = new Google_Service_Gmail($client);
    $email = new Google_Service_Gmail_Message();

    $string = "From: noreply@example.com\r\n";
    $string .= "Content-type: text/html;charset=iso-8859-1\r\n";
    $string .= "Subject: $subject\r\n";
    $string .= "$body\r\n";

    $email->setRaw($string);
    $service->users_messages->send('me', $email);
}

send_email('subject', 'body');