code: public function getBaseData()
      {
          $data = new FluidXml(false);
  
          $message = $data->addChild('Message', ['version' => $this->getApiVersion()], true);
  
          $header = $message->addChild('Header', true);
          $header->addChild('Time', $this->getTime());
  
          $itentity = $header->addChild('Identity', true);
          $itentity->addChild('UserID', $this->getUserId());
  
          $body = $message->addChild('Body', ['type' => 'GetInvoice', 'live' => $this->getLive()], true);
          $order = $body->addChild('Order', ['paymentMethod' => $this->getPaymentMethod()], true);
  
          $order->addChild('MerchantID', $this->getMerchantId());
          $order->addChild('SiteAddress', $this->getSiteAddress());
          $order->addChild('PostbackURL', $this->getNotifyUrl());
          $order->addChild('SuccessURL', $this->getReturnUrl());
          $order->addChild('FailureURL', $this->getCancelUrl());
  
          return $message;
      }
docs: Get base data
  @return FluidXml