public function createUrl() {
    $string_data = $this->dataToString();
    $data_to_send = array(
      'hash' => $this->doHash($string_data),
    );
    // Adicionalmente adjuntamos el resto de los valores iniciados en $data
    foreach ($this->data as $name => $value) {
      $data_to_send[$name] = $value;
    }
    $data_to_send['agent'] = $this->agent;

    // Iniciamos CURL
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $this->apiUrl);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POST, TRUE);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $data_to_send);

    $output = curl_exec($ch);
    $info = curl_getinfo($ch);
    curl_close($ch);
    if ($info['http_code'] == 200) {
      return $output;
    }
    else {
      return FALSE;
    }
  }