Who Can and How to Apply to Use This Feature?

The standard e-invoice in the National e-Invoicing System (KSeF) has a strictly defined structure. However, what if your company needs to provide clients with much more detailed data, such as utility usage statements or telecommunication bills? This is precisely why the Ministry of Finance has prepared a special functionality – the invoices with an attachments in KSeF.

What are invoices with attachments in KSeF?

This functionality allows you to include additional, structured data with a standard e-invoice.
Undoubtedly, this is a response to the needs of entrepreneurs who previously included extensive attachments with detailed billing information.
Furthermore, an attachment in KSeF is not just any file (like a PDF or JPG).
In fact, it is an integral, structured part of the invoice’s XML file.
Specifically, it is used exclusively to detail the data related to invoice items.

Who can use this option?

The ability to send invoices with attachments was created primarily for industries that generate invoices with a very large amount of detailed data. These mainly include:

• Firstly, utility providers.
• Secondly, telecommunication companies.
• Finally, fuel suppliers issuing collective invoices.

This functionality is, however, available to any other industry,

provided that it meets the statutory requirement concerning “activities with a complex number of data”.

Applying to Send Invoices with Attachments in KSeF

The ability to send invoices with attachments is not enabled by default.

Therefore, to activate it, you must submit a special application.

• When to apply? The application service will be available from January 1, 2026, and the functionality itself from February 1, 2026. You should apply before you plan to start issuing this type of invoice.
• Where to apply? You can only submit the application through your account in the e-Tax Office (e-Urząd Skarbowy).
• What does the application contain? Besides your company’s data, you must declare, among other things, that the invoices will concern activities with a complex number of data.
• Confirmation: Subsequently, after submitting the application, you will receive an activation confirmation to the provided email address within a maximum of 3 business days.

Summary

In conclusion, invoices with attachments in KSeF are an important functionality for a specific group of entrepreneurs. However, remember the key rules:

1. This is a non-default option and requires a special application.
2. The attachment has a strictly defined, technical function.
3. You will need commercial software to handle it; the free tools from the Ministry of Finance will not support this feature for issuing.

If this topic concerns your company, we invite you to contact us. Our professional accounting office will help you implement all the necessary procedures.

www.luno-group.com

In our next post, you will learn how to issue your first invoice in KSeF.