Fields in KSeF – What you need to know

April 28, 2025

The National e-Invoicing System (KSeF) is a platform that introduces standardization in issuing and receiving invoices in Poland. For companies using the SAP system, understanding and correctly filling in the fields in KSeF is crucial to ensure compliance with regulations and effective management of financial documentation. In this article, we explain what fields are present in the KSeF system, what their types are, and what errors may occur when filling them in.

Types of fields in KSeF

In the KSeF system, several categories of fields are distinguished that are required for correctly issuing an invoice:

Mandatory Fields

These are fields that must be completed for the invoice to be sent to KSeF. If data is missing in these fields, the invoice will be rejected by the system.

Examples of mandatory fields:

Seller’s and buyer’s tax ID (NIP)
Invoice number
Invoice issue date
Net amount, VAT, and gross amount
VAT rate

Optional Fields

These fields may be completed if they are relevant to the specific transaction or are important for accounting documentation. Their absence does not affect the ability to send the invoice to KSeF.

Examples of optional fields:

Customer order number
Additional information about goods or services
Comments regarding the transaction

Fields depending on the type of Invoice

Some fields are required only for specific types of invoices, such as advance or corrective invoices.

Examples of dependent fields:

Date of delivery or service completion (for advance invoices)
Original invoice number (for corrective invoices)
Reason for correction (for corrective invoices)

Logical structure of fields in KSeF

Each invoice in KSeF is saved in a logical structure that defines how data is presented in XML format. For the user, this means the accounting or ERP system must be adapted to KSeF’s technical requirements.

Key structure elements:

Invoice header:

Invoice number
Issue date
Seller’s and buyer’s data

Invoice items:

Description of goods/services
Quantity
Net unit price
VAT rate

Invoice summary:

Net amount
VAT amount (broken down by rates)
Gross amount

Each invoice in KSeF is stored in XML format. The document’s logical structure defines how the data should be presented. For SAP users, this means the need to install an add-on to the ERP system.

Main parts of the invoice:

Header: invoice number, dates, contractor data
Items: description of goods/services, quantity, net price, VAT
Summary: net amounts, VAT by rate, gross

KSeF fields in SAP – Integration and challenges

Companies using SAP should ensure that the field structure in the e-invoice fully complies with KSeF requirements. Integrating SAP with KSeF involves:

Mapping XML fields to SAP form fields
Automatically generating invoices from SAP
Digitally signing and sending documents to KSeF
Receiving UPO (official confirmation of receipt) and processing feedback messages

Most common errors – How to avoid them?

Missing mandatory data – results in invoice rejection
Data format errors – e.g., incorrect dates or numbers
Non-compliance with regulations – e.g., wrong VAT rate

Recommendations:

Test XML files for correctness before sending
Add dedicated controls and approval for sending
Educate your team – knowledge of FA(3) is now mandatory

New: FA(3) structure and attachments

In 2024, a new FA(3) structure was introduced, allowing, among others, the addition of attachments to e-invoices. This is especially important for companies operating in service industries that generate additional documentation.

How to prepare SAP for KSeF?

Choose the right integrator, assign the configuration to experts
Implement solutions that automate data reading and sending to KSeF
Ensure compliance with the FA(3) schema

Trust Our KSeF and SAP Experts

We specialize in implementing KSeF in the SAP environment. Contact us if you want to be sure your system operates in accordance with current regulations and is ready for future changes.