FA(3) in KSeF — What Is the New Logical Invoice Structure?
Many people talk about KSeF as if it were simply about "sending invoices to the system". In reality the entire operation is built on something considerably more technical: the logical structure of the structured invoice.
Since 1 February 2026 the operative standard is FA(3). If you use invoicing software or are planning a KSeF integration, this topic is critical.
What Is the FA(3) Logical Structure?
FA(3) is the official invoice data template used in KSeF. It defines which fields an invoice may or must contain, how data is recorded, and what the technical structure of the document looks like.
Put simply:
- a PDF shows you how an invoice looks,
- FA(3) defines how an invoice is built internally.
When Does FA(3) Apply?
From 1 February 2026, all structured invoices issued through KSeF must use the FA(3) logical structure exclusively.
This means businesses and software providers must work with the current template. Using outdated schemas can lead to errors or non-compliance with KSeF requirements.
What Does FA(3) Change in Practice?
For business owners, three things matter most:
1. Your invoicing software must comply with the current structure
If your system does not support FA(3), there is a risk of errors or non-compliance with KSeF.
2. The accounting integration must be up to date
Having "some integration" is not enough. It must match the current requirements.
3. Company procedures should reflect the new document logic
This includes corrections, offline modes, and data flows between departments.
Does Every Business Owner Need to Understand the Technical Details of FA(3)?
Not every company owner needs to read an XML schema over morning coffee. But everyone should know that:
- a logical structure exists,
- FA(3) has been in force since 1 February 2026,
- their software must comply with the current standard.
Otherwise it is easy to fall into the trap of assuming that "the software issues invoices, so everything must be fine". In a real KSeF rollout, that assumption can be expensive.
Who Is Most Affected by FA(3)?
The topic is particularly important for:
- software providers,
- accounting offices,
- companies with automated document workflows,
- business owners who want to avoid problems after KSeF implementation,
- both companies and sole traders issuing large volumes of invoices.
How to Check Whether Your Business Is Ready for FA(3)
A simple checklist:
- does the software support KSeF 2.0,
- has the provider confirmed compliance with FA(3),
- have you tested issuing and receiving documents,
- does your accountant understand how the new template works,
- do your procedures reflect the current operating model.
Key Takeaway
FA(3) is not a "technical detail for IT teams". It is the foundation of how an invoice functions in KSeF. If a company's system is not compliant with the current structure, the entire process can start falling apart faster than a paper folder meets a cup of coffee.
Tax and e-invoicing rules in Poland change frequently. Always verify current requirements with a licensed accountant or at podatki.gov.pl.