private function send_mail_with_sendinblue_api($demand)
 {
     $config = new Config();
     $sendinblue_token = $config->get_sendinblue_connection();
     $mailin = new Mailinblue("https://api.sendinblue.com/v2.0", $sendinblue_token);
     $data = array("id" => 3, "to" => $demand->email, "attr" => array("USERNAME" => $demand->name_and_surnames, "SUBJECT" => "Tu peticion de servicio en 123mecanico.es", "CONTENT" => $this->build_html_content($demand)));
     $res = $mailin->send_transactional_template($data);
     return $res;
 }