Integration of SAP ERP System with External Invoicing System Via SAP XI

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Key Takeaways

⇨ The SAP XI system is an exchange infrastructure between SAP ERP and the external invoicing system.

⇨ When using an external system, it is necessary to use up-to-date and detailed information about orders.

⇨ Users must create functional modules and tables to receive and send data to SAP ERP.

When the SAP ERP system was implemented in an enterprise in the EU, clients used, among other things, the Ascendo invoice accounting system in the existing system landscape. It is intended for the following functions:

  • scanning and loading printed forms of invoices received from suppliers
  • data recognition
  • the formation of an invoice document
  • define account assignment parameters
  • reconciliation and posting of an invoice
  • the formation of payment documents

Our project team from SAP-side implemented integration with this system. Developments for integration from the external system were conducted by a group from Ascendo.


The SAP XI system was used as an exchange infrastructure between SAP ERP and the external invoicing system. Functional modules were developed, which pushed data from SAP ERP to SAP XI so it could pass to the external system and also receive data from SAP XI in SAP ERP and form documents based on them.

The integration process from a technical point of view included:

  • The main SAP ERP system
  • External system for the formation and release of Ascendo invoices
  • SAP XI exchange system

From an organizational point of view, the process was divided into:

  • Exchange of master data in manual or automatic mode
  • Formation of invoices using purchase orders
  • Formation of invoices without the use of purchase orders

From the point of view of the user interface, the following objects were used in the exchange process:

  • Standard transactions SAP ERP for the maintenance of master data
  • A general corporate interface for maintaining additional settings in SAP ERP
  • Standard SAP ERP transactions for the creating of purchase orders, goods receipts (services)
  • Standard XI monitor and developed transaction in the SAP ERP of the integration monitor
  • Standard functionality of SAP XI
  • External system for the formation and release of invoices

Master Data for Exchange

It was intended to exchange the following data as master data (Figure 1):

  • Account Assignment Objects:
    • General ledger accounts
    • Cost centers
    • Plant maintenance orders, controlling orders, production orders, sales orders
    • WBS-elements
  • Purchasing groups
  • Vendor masters
  • Codes and rates of currencies

The GL accounts of material-stock are used as an account assignment for goods receipt to the warehouse. Also, the purchasing group was used as an additional sign-in account assignment in all invoices. It corresponded to the subdivision – the applicant of the requirements or the warehouse. For services and investments, the classic account assignment objects were used.

The composition and format of these master data in SAP ERP and the external system was synchronized. Some of the master data was adapted through intermediate tables. For example, the code for some GL accounts in Ascendo consisted of four characters – the vendor code consisted of connecting the fields of the supplier’s number, country, and bank account number. Further synchronization of master data was assumed based on the results of running periodic tasks for the execution of functional modules in SAP ERP. The updated data tables were transferred through the SAP XI to the external system.

The functional modules responsible for downloading the master data had tuning parameters. Organizational levels and frequency of exchange for the transmitted data can be configured through the corporate-wide configuration management interface (ZSPRO). The purchasing group table is rarely changeable, so it was downloaded to the external system and it is supposed to be manually updated.

Figure 1. Transferring the master data to the external system.

Chain Using the Purchase Order

Most purchases of materials and services in the enterprise are expected through the creation of a purchase order in the SAP ERP system. Goods receipts or services entry sheets are also generated only in SAP ERP. However, in the external system it is necessary to use up-to-date and detailed information about orders. Each time an order or material document is saved, that initiates the launch of a functional module for transferring data from the purchase order and from the material document. In this way, changes in orders and the entire history of PO items, including reversing documents, are also transmitted.

Figure 2 shows the scheme for generating an invoice using a purchase order. After receiving data from SAP and from the supplier from the incoming invoice, these data are compared in the Ascendo system. The user exercising (controlling) such binding checks the accuracy of account assignment, amounts, and other attributes. If the result of the check is positive, the invoice in Ascendo is sent for approval. At the same time, data is sent from Ascendo to SAP in the form of an XML file corresponding to the saved invoice. This received package starts the execution of the function module in the SAP ERP, creating a parked invoice in SAP. This function module is based on BAPI_INCOMINGINVOICE_CREATE1.

Based on the results of the creation of a parked invoice from SAP to Ascendo, confirmation comes to change the status of the invoice. After approval of the invoice to Ascendo, a message is sent to SAP ERP where the function module posts the parked invoice. The functionality also includes the possibility of rejecting the invoice during the reconciliation process. Cancelation of the invoice and subsequent creation of the corrective is performed only for technical purposes in SAP ERP using standard transactions.

Figure 2. Generating invoices for purchase orders.

Mapping Data

The data received from SAP was automatically matched against the data obtained from the invoice scan by the SAP purchase order number or manually through the search for other attributes. (See table 1).

Data in Ascendo from SAP Data in Ascendo from vendor
Organizational data of the company (company code) Organizational data of the company (company code)
Numbers of purchase order/item, addition numbers
PO date, goods receipt date PO date, invoice date
Information about the supplier Information about the supplier
Terms of payment Terms of payment
Currency Currency
ID and text of the material (service) ID and text of the material (service)
Actual quantity, unit of measure, value from the goods receipt from the order item Actual quantity, unit of measure, value from the invoice items
Account assignment (GL-account, cost center, internal order, WBS-element, purchasing group)
Scan-copy of original invoice


Table 1. Mapping data from SAP and from the vendor from Ascendo.

The Ascendo system works through the WEB-interface. The Matched data of header looks in the interface, as shown in Figure 3.

Figure 3. Matching of the headers data of invoice and data from SAP in the Ascendo system.

When you assign data to the Ascendo invoice from the SAP purchase order, the item data is also pulled up. In Figure 4, you can see an example for material items. In this case, the “Material data” tab contains lines that indicate:

  • Purchase order number
  • Material number
  • Quantity
  • Price
  • Value
  • Order item number
  • Text of PO-item
  • Goods receipt item number, composed of several numbers
  • User

Figure 4. An example of the obtained item data items from SAP.

Account assignment data is also transferred from SAP. For materials arriving at the warehouse (Figure 5) you can see the stock GL account number from four symbols, the purchasing group code of the corresponding unit (warehouse or workshop), the cost of the item, and the login of the approval user. In addition, there is a line in which you can specify deviations between the cost of the order (goods receipt) and the invoice.

Figure 5. An example of the received account assignment data from PO-items of SAP.

Figure 6 shows an example of data transferring PO item with service from SAP to Ascendo. The transmitted information is like the material items. In this case, the service number is transmitted instead of the material number. The number of the automatically generated goods receipt document consists of the purchase order number, the number of the PO-item, the year of the material document, the material document number, and the item number of the material document.

For example: 25006392950001020185003283530-0001

Figure 6. Example of received PO-item with service from SAP.

The traditional account assignment is necessarily transferred for services, among other things. In this case, this is a plant maintenance order 835010002155. In the Ascendo interface, you can see this on another tab, Figure 7. The general ledger account 3209020011 is automatically converted to Ascendo GL account 5513 by mapping table. The purchasing group KPM corresponds to a certain subdivision (workshop). The first line of the account assignment displays the VAT amount and the GL account 2641 for its accounting.

Figure 7. An example of the received account assignment data for services items from SAP.

The corresponding function module in the SAP ERP system creates a parked invoice after saving the invoice and sending it for approval. Then after approval in Ascendo, the invoice is posted in the SAP ERP. Figure 8 shows the posted invoice. It been created in SAP ERP for the purchase order for services, based on integration with Ascendo.

Figure 8. An example of the invoice created in SAP ERP based from Ascendo data.

Document Chain

Some periodically purchased services under master contracts (electricity, water, rent) are issued in SAP without a purchase order (Figure 9). In this case, the pre-configured account assignment variant (cost center, GL-account, purchasing group) and data from supplier invoice are matched by financial manager in Ascendo. After entering the account assignment and checking the invoice, the user saves it. An XML file is then created in Ascendo and sent to SAP.

Next, the function module in the SAP ERP creates a preliminary act with reference to the contract (Z-document) based on the received XML file. At the same time, if you save to Ascendo, the invoice is sent there for approval. After full agreement in Ascendo the second XML-file is transferred to SAP ERP. Based on the second XML file, the function module in SAP creates an accounting document – an invoice posting. After the creation in SAP ERP of the preliminary act and the accounting document in Ascendo, a report on the successful action is received from SAP and this changes the status of the invoice.

Figure 9. Generating invoices without purchase orders.

In Figure 10, you can see the integration of the invoice in Ascendo and the automatically created on its basis an accounting document in SAP. It also includes a link to the contract and additional numbers. SAP ERP also automatically creates a controlling document.

Figure 10. Example of data mapping of Ascendo-SAP without a purchase order.

To receive and send data to SAP ERP, functional modules and tables were created that contained received or transmitted data. For the convenience of tracking the status of documents, as well as for the convenience of correcting wrong situations, the transaction “Integration Monitor” was developed in SAP ERP. The monitor was especially useful during the testing of complex examples.

With the help of this functionality, it was possible to simulate a certain action in the Ascendo system without having the technical ability to fully study the “foreign side” when integrating systems. In addition, we used the functionality of SAP XI, which allowed us to analyze the status of the exchange. Figure 11 shows the interface of the integration monitor.

Figure 11. The interface of the integration monitor in SAP ERP.


Integration of SAP ERP with the external invoicing system of Ascendo was launched from the time of the general Go-Live productive start (January). Three months of pilot operation of the SAP ERP system showed good performance. Ascendo is used by one user from the financial department and by the CEO who personally approves certain invoices.

Verification of the comparison of data received from SAP and data from the incoming invoice from the supplier was the most time-consuming part for users at the initial stage. However, this allowed for regulation of the order, to eliminate the existing gap between the received and paid invoices, and the corresponding operations for the purchase of materials and services.

As of 2023, the system has been completely transferred to support mode and successfully used for a long time.


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