the new concept for the functioning of the e-invoice attachment for KSeF

New concept for the functioning of the e-invoice attachment in KSeF 

The new FA(3) logical structure and e-invoice attachments in KSeF

The possibility of sending e-invoices with attachments will be an additional functionality of the KSeF system. In this respect, the Ministry of Finance has listened to the demands of entrepreneurs. Find out how this solution is going to work. 

The concept for the functioning of the e-invoice attachment – key information

It will be possible to add one attachment to each invoice issued via the National e-Invoice System (KSeF). Despite this limitation, the solution is quite flexible, as the attachment can contain multiple data blocks presented in a tabular format. The structure of such a table allows inserting up to 20 distinct columns with individual headers. 

In addition to columns, the data table can include rows, along with a table summary. This enables entering data row by row, making it possible to adapt the table’s dimensions to the specific needs of a business. 

This solution will be especially useful when sending invoices for the supply of utilities such as electricity or gas. It will be possible to include data on utility consumption broken down by individual collection points. Telecommunications companies have also advocated for this functionality. In their case, the table will contain detailed information related to the services provided. 

Another group of companies that will benefit from these changes are fuel suppliers. It will be possible to issue collective invoices for fuel used by an entire fleet of vehicles, as the attachment will allow purchases to be assigned to individual vehicles. 

Who will benefit from issuing e-invoices with attachments

From a technical standpoint, there are no restrictions on the use of invoice attachments. This functionality can be useful not only for utilities, telecommunications companies, and fuel suppliers but anyone required to issue invoices through KSeF. 

It is important to note that the attachment must be in the form of a table which will be an integral part of the invoice. Both the invoice and the attachment will be included in the same XML file. It will not be possible to add attachments in formats such as PDF or JPG. 

Using attachments for marketing or business purposes is prohibited. Commercial information, such as price lists or information concerning promotions or sales are not allowed to be sent this way. Similarly, it is also not allowed to use this functionality for sending newsletters, orders, warranty terms or user manuals. Acceptance protocols, annexes to contracts or contracts themselves cannot appear in the attachment either. 

Attachments to structured invoices – technical aspects

The maximum size of an e-invoice, including the attachment, is 3 MB. However, it is important to keep in mind that this limitation only applies to invoices with an attachment. The permissible size of an invoice without an attachment hasn’t been changed and still equals 1MB. 

An invoice with an attachment will be stored in KSeF for 10 years, just like an invoice without an attachment. This period will be counted from the end of the year in which the invoice was issued. 

Since the attachment and the invoice are treated as a whole, if any errors appear in the attachment, issuing a corrective invoice will be necessary. Such a document must include the KSeF number of the invoice being corrected.  

Importantly, the option to send invoice attachments will only be available after an application has been submitted. An entrepreneur wishing to use such a feature must submit a request via KSeF and then wait for its approval. 

The approval process is expected to take up to 30 days but may be extended in particular cases, such as when the entrepreneur indicates an unusually large number of invoices with attachments that they are planning to send via KSeF. Therefore, it is advisable to make such requests well in advance. 

According to the Ministry of Finance, even though it will be possible to send invoices with attachments from February 1, 2026, the application itself must be sent before that date. The KSeF API will be prepared to support this process in advance. 

Sending e-invoices with attachments will only be possible by using the API. Free tools provided by the Ministry of Finance will not provide this feature.  

If you are planning to send invoices with attachments using the SAP software, we encourage you to take advantage of our offer. We will help you seamlessly implement the changes required to transmit invoices through the National e-Invoice System (KSeF). 

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