With the introduction of the National e-Invoicing System (KSeF), the invoicing process in Poland is undergoing a major transformation. The new regulations mean not only the need to comply with legal requirements but also to meet specific technical standards – particularly for companies using ERP systems such as SAP. One of the key components of the e-invoice structure in KSeF is the so-called declared data. These are the elements that determine whether a document will be properly processed and accepted by the system. In this article, we explain what declared data in KSeF is, its function, and why accuracy is especially critical in the SAP environment.
What is declared data in KSeF?
Declared data includes all the information that, according to the logical structure of the e-invoice, must or may be included in a document sent to KSeF. This structure is defined in the XML schema (XSD) provided by the Ministry of Finance.
There are three main categories of data:
- Mandatory – without them, the invoice cannot be submitted (e.g. buyer’s VAT ID – NIP),
- Optional – recommended but not required (e.g. purchase order number),
- Context-dependent – required only in specific cases (e.g. for advance or summary invoices).
Key groups of declared data
Below are the essential elements that should be present in an e-invoice structure in KSeF:
1. Party identification data
- Seller and buyer VAT ID (NIP),
- Full name of the entity,
- Registered office or branch address.
2. Transaction information
- Invoice issue date,
- Delivery or service completion date,
- Invoice number.
3. Line item details
- Description of the goods or services,
- Quantity and unit of measure,
- Net unit price,
- Net, VAT, and gross amounts.
4. Document summary
- Total net value,
- VAT amounts by applicable rates,
- Total gross value.
5. Additional data (optional)
- Purchase order number,
- Transaction notes,
- Industry-specific info (e.g., logistics data).
The importance of declared data in practice
Declared data is essential for:
- Correct tax settlements – completeness directly affects VAT return compliance,
- Consistency in accounting and purchasing processes – especially with full SAP-KSeF integration,
- Automation – correct data structure allows ERP systems to function without manual intervention or EDIFACT interfaces,
- Transaction transparency and security – facilitates audits, inspections, and compliance with Ministry of Finance standards.
The role of FA(3) schema in KSeF declared data
Understanding the changes introduced by the FA(3) schema is crucial when working with declared data in KSeF. The new version of the schema, expected in 2025, expands the scope of data that can be included in e-invoices, allowing for more detailed transaction descriptions. This is particularly valuable for companies using ERP systems like SAP, as it enables better integration and automation of accounting processes.
FA(3) also introduces the possibility of attaching documents to invoices – a feature addressing the needs of businesses that require additional documentation as part of the e-invoicing process. To use this functionality, a prior declaration and automatic system approval will be required.
For a more detailed discussion of FA(3) changes and their impact on SAP, see our article:
Final consultations on KSeF and the new FA(3) logical structure
Common mistakes in declared data
In practice, the most common reasons for invoice rejection by KSeF include:
- Missing required data (e.g. NIP, issue date),
- Incorrect data format (e.g. currency code not conforming to ISO),
- Misplacement of data within the XML structure,
- Outdated or incorrect contractor information (e.g. typos, wrong address),
- Duplicate invoice number sent again from SAP to KSeF.
Ensuring data accuracy in SAP
For companies using SAP, proper system preparation for KSeF integration is essential. Consider the following:
1. Direct SAP-KSeF integration (no proxy)
This allows for direct e-invoice submission to KSeF without intermediaries, reducing the risk of system failure and simplifying diagnostics.
2. Data validation before sending
SAP should allow for checking data completeness at the entry or approval stage.
3. Support for corrections (e.g. from Credit Notes)
Your solution should allow for making corrections to invoices even if the amounts haven’t changed (e.g., payment term extension). Such corrections may require functionality beyond the default SAP modules.
You can find more information about KSeF on the official government website.
Declared data is not just a technical aspect of invoicing – it’s a prerequisite for proper document processing in KSeF. Their completeness, accuracy, and quality directly impact transaction security, tax compliance, and the success of SAP integration.
Looking for a technology partner for KSeF implementation in SAP?
At Haergi, we specialize in SAP-KSeF integrations, invoicing automation, and data compliance analysis. We manage end-to-end projects – from audit and configuration to testing and post-implementation support.
Get in touch with our team to learn how to prepare your company for full KSeF compliance.
