code: public function getData()
      {
          $this->validate(
              'merchantId',
              'merchantAccountNumber',
              'customerIdAtMerchant',
              'transactionId',
              'amount',
              'currency'
          );
  
          $data = array();
          $data['PaymentPageID'] = $this->getMerchantId();
          $data['MerchantAccountNumber'] = $this->getMerchantAccountNumber();
          $data['CustomerIdAtMerchant'] = $this->getCustomerIdAtMerchant();
          $data['TxID'] = $this->getTransactionId();
          $data['Amount'] = $this->getAmount();
          $data['Currency'] = $this->getCurrency();
          $data['MerchantFreeText'] = $this->getDescription();
  
          if ($returnUrl = $this->getReturnUrl()) {
              $data['OnSuccessUrl'] = $returnUrl;
          }
  
          if ($cancelUrl = $this->getCancelUrl()) {
              $data['OnFailureUrl'] = $cancelUrl;
          }
  
          if ($notifyUrl = $this->getNotifyUrl()) {
              $data['TransferUrl'] = $notifyUrl;
          }
  
          $data['Checksum'] = $this->calculateArrayChecksum($data);
          return $data;
      }
docs: Get the data for this request.
  
  @return array request data