Structured Invoice – What It Is and How It Works in KSeF

From February 2026, Polish companies transition to mandatory e-invoices. The central element of this change is the structured invoice. We explain exactly what this document is, how it looks, and how it differs from a regular PDF invoice.

What Is a Structured Invoice?

A structured invoice is an XML format document issued through the National e-Invoice System (KSeF). Upon issuance, the system automatically assigns it a unique identification number, called the KSeF number. This is the official definition in accordance with Article 2, point 32a of the VAT Act.

In practice, this means that an invoice is no longer just a PDF file sent by email. It's an organized set of data saved in a standard XML format that the Ministry of Finance system understands. Such a document is automatically stored in the central database for 10 years and is immediately available to your counterparty – you don't need to send it yourself.

What Does the Invoice Structure Look Like?

From February 1, 2026, the logical structure FA(3) is mandatory. This is a strictly defined template that specifies what data and in what order must be included in the XML file. You don't download this template and fill it out manually – it's implemented in your accounting software, which automatically generates the invoice according to these rules.

The FA(3) structure introduces one important novelty: the "Attachment" element. It allows you to send additional data together with the invoice, but only after reporting this to the e-Tax Office. However, remember that the attachment must be an integral part of the XML file. You cannot send separate files like PDF, JPG, or XLS to KSeF – you can of course send such documents to your counterparty, but through traditional means, outside the system.

How Does Issuing a Structured Invoice Work?

The process is simpler than it seems. You issue an invoice in your accounting software just as you did before. You assign it your internal number, which identifies the document in your system (saved in field P_2 of the XML structure). Then the software automatically sends the document to KSeF.

At this point, the system verifies whether the invoice complies with the logical structure FA(3). If everything matches, it assigns a unique KSeF number and sends you back an Official Receipt Confirmation (UPO). This is confirmation that the invoice has been accepted. From this moment, the document is automatically visible to your counterparty in their KSeF panel – you don't need to send it anywhere.

Two Numbers – What's the Difference?

Here's an often confused aspect: an invoice has two different numbers. The first is your internal invoice number (e.g., FV/2026/01/001), which you assign in the accounting software and which is saved in field P_2 of the XML structure. The second is the KSeF number – a unique identifier assigned by the system after accepting the invoice. This second number is returned in the UPO and is not part of the XML file itself.

Both numbers may appear on the printout or visualization of the invoice – your internal number and the KSeF number. This is normal and helps identify the document both in your system and in the ministry's system. The KSeF number consists of several parts and always starts with the year of issue, for example: 2026-04-15-ABC123456-XYZ789.

What Invoices Can Be Issued as Structured Invoices?

In KSeF, you can issue practically all types of VAT invoices: basic, advance, settlement, and all types of corrective invoices. The system also supports simplified invoices. This covers the vast majority of entrepreneurs' daily needs.

However, there are documents that you cannot issue in KSeF. The system doesn't support internal evidence, receipts within the meaning of the Tax Ordinance, pro forma invoices, or debit and credit notes. You must transmit these documents to counterparties by other means – so it's worth planning how this process will look in your company after implementing mandatory KSeF.

Consumer Invoices – Exception to the Rule

Invoices issued to natural persons not conducting business activity are not subject to mandatory KSeF. You can issue them in the system voluntarily, but if you decide to do so, you must provide the consumer with access to the invoice. This is most often done by providing a visualization with a QR code that allows verification of the invoice in the system.

This solution provides flexibility – if your business is mainly based on sales to consumers, you don't have to immediately implement KSeF for all transactions. You can gradually transition to the new system or remain with current methods for individual customers, focusing on mandatory KSeF only for B2B transactions.

Summary

A structured invoice is nothing more than an XML document issued through KSeF and marked with a unique number. It differs from a traditional PDF invoice in that it has a strictly defined structure, is automatically stored in the system, and is immediately available to the counterparty. In practice, this means the end of sending invoices by email and storing piles of PDFs – everything happens automatically in the central system.

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Source: https://ksef.podatki.gov.pl/