static public function isPaymentMethod($paymentMethod) {
    return ((string) $paymentMethod == Connect2PayClient::PAYMENT_METHOD_CREDITCARD ||
        (string) $paymentMethod == Connect2PayClient::PAYMENT_METHOD_TODITOCASH ||
        (string) $paymentMethod == Connect2PayClient::PAYMENT_METHOD_BANKTRANSFER ||
        (string) $paymentMethod == Connect2PayClient::PAYMENT_METHOD_DIRECTDEBIT ||
        (string) $paymentMethod == Connect2PayClient::PAYMENT_METHOD_WECHAT ||
        (string) $paymentMethod == Connect2PayClient::PAYMENT_METHOD_LINE ||
        (string) $paymentMethod == Connect2PayClient::PAYMENT_METHOD_ALIPAY);
  }