Invoices with Attachments in KSeF 2.0 – Remember to report

As of 1 January 2026, the Ministry of Finance has made available a new functionality within the National e-Invoicing System (KSeF 2.0), enabling the issuance and submission of structured invoices containing an attachment. This solution responds to requests raised by entrepreneurs during public consultations related to the mandatory implementation of KSeF. It should be emphasized that the use of attachments is not mandatory and will be available exclusively to taxpayers who submit the relevant notification and obtain its approval.

Notification of the Intention to Issue Invoices with Attachments

In order to use the new functionality, it is necessary to submit a notification via the e-Tax Office (e-Urząd Skarbowy). The notification form includes, in particular:

• the taxpayer’s identification data and email address,

• the type of transactions to be documented with invoices containing attachments,

• justification for the need to use attachments,

• estimated technical parameters, including the average monthly number of invoices and their approximate file size.

The notification may be submitted:

• directly by a taxpayer who is a natural person, or

• by an authorised User of the Organisation Account (UOA) – in the case of legal entities and other organisational units.

Notifications are processed in the order in which they are received, and the maximum processing time is 3 business days (subject to exceptional circumstances). Information regarding the status of the notification is provided electronically.

Discontinuation of Issuing Invoices with Attachments

A taxpayer who decides to cease issuing invoices with attachments is required to submit an appropriate notification via the e-Tax Office. Following its processing, the taxpayer will remain entitled to issue invoices in KSeF, albeit without the attachment functionality.

Nature and Scope of Data Included in the Attachment

The attachment constitutes an integral part of the structured invoice (XML file) and may not be submitted as a separate file (e.g. PDF or JPG). Only the following information may be included in the attachment:

• data of a tax-related nature,

• information directly linked to price, unit of measure and quantity of goods or services,

• industry-specific data accompanying tax information (e.g. metering point numbers, meter data, vehicle registration numbers).

Attachments must not be used to transmit marketing, commercial or contractual materials, such as agreements, acceptance protocols, price lists or commercial offers. Breach of these rules may result in withdrawal of the taxpayer’s right to use the attachment functionality.

Attachment as an Element of the FA(3) Structure

The new FA(3) logical structure has been extended to include an optional “Attachment” node. This allows for the presentation of data in flexible table formats, including column headers, rows and summary sections. Each structured invoice may contain one attachment, which may consist of multiple data blocks.

Technical and Organisational Aspects

• maximum size of an invoice with an attachment: 3 MB,

• maximum size of an invoice without an attachment: 1 MB,

• invoice retention period in KSeF: 10 years,

• any error in the attachment requires the issuance of a correcting invoice,

• the functionality is available only upon approval of the notification and for a period of 2 years (after which a new notification must be submitted).

Free tools provided by the Ministry of Finance will allow users to view and download invoices with attachments, but will not support the creation or submission of such invoices. This functionality is intended for users of commercial accounting and ERP systems integrated with the KSeF API.

The introduction of invoice attachments within KSeF represents a significant facilitation for businesses operating with complex settlement data, particularly in sectors such as energy, telecommunications and fuel distribution. At the same time, the solution remains optional and requires appropriate organisational and technical preparation.

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