static public function isPaymentMode($paymentMode) {
    return ((string) $paymentMode == Connect2PayClient::PAYMENT_MODE_SINGLE ||
        (string) $paymentMode == Connect2PayClient::PAYMENT_MODE_ONSHIPPING ||
        (string) $paymentMode == Connect2PayClient::PAYMENT_MODE_RECURRENT ||
        (string) $paymentMode == Connect2PayClient::PAYMENT_MODE_INSTALMENTS);
  }