The mandatory use of the National e-Invoicing System (KSeF) was intended to standardize the invoicing process and streamline the circulation of invoices. In practice, however, situations may arise in which the system’s technical limitations make it difficult to comply with the requirements of the VAT Act. In an individual tax ruling of 16 July 2026, ref. no. 0112-KDIL1-1.4012.348.2026.1.JKU, the Director of the National Tax Information (KIS) addressed the possibility of using external attachments to collective corrective invoices issued through KSeF.
The applicant was a company engaged in the wholesale distribution of food products. Due to the scale of its business, the company issues a very large number of sales invoices and subsequently prepares numerous collective corrections related, among other things, to discounts, bonuses and transfer pricing adjustments. Such corrections may cover even several tens of thousands of original invoices.
After becoming subject to the KSeF obligation, the company found that although the logical structure of the system allows up to 50,000 corrected invoices to be indicated, the 1 MB XML file size limit makes it practically impossible to use this limit. As a result, issuing such collective corrective invoices encountered technical limitations of the system. The first collective corrective invoice prepared by the company exceeded 9 MB, while the largest corrections covered as many as 49,000 original invoices. In the company’s view, splitting such corrections into smaller documents was technically and organizationally impractical and could also result in the KSeF API limits being exceeded.
The company therefore planned to include in the KSeF structure only part of the required references to the corrected invoices, to the extent necessary to remain within the file size limit. The complete list of invoices covered by the correction would instead be provided to the purchaser in a separate attachment sent outside KSeF. The attachment was intended to constitute an integral part of the corrective invoice and contain data enabling it to be unambiguously linked to that invoice.
The applicant asked whether such a solution would be sufficient to meet the requirements of Article 106j of the VAT Act, particularly with regard to providing information identifying the corrected invoices, such as their issue dates, invoice numbers and KSeF identification numbers, where assigned.
The company argued that the VAT Act specifies the information that must be included in a corrective invoice but does not determine how that information must be arranged. It also emphasized that the proposed solution would not result in any required information being omitted. All data concerning the corrected invoices would be provided to the purchaser, although some of it would be transmitted outside KSeF due to the system’s technical limitations.
The company also pointed out that, before mandatory KSeF was introduced, tax authorities had repeatedly accepted the possibility of including certain information in attachments forming an integral part of an invoice. In its view, the same approach should be permissible after the introduction of mandatory KSeF, particularly since the need to use an external attachment resulted solely from the system’s technical limitations and not from any action on the part of the taxpayer.
The company further argued that a different approach would result in taxpayers bearing the negative consequences of functional limitations of a telecommunications system beyond their control. It also referred to the principle of proportionality and the case law of the Court of Justice of the European Union, arguing that measures adopted by Member States should not go beyond what is necessary to ensure the proper collection of tax.
The Director of KIS did not agree with this position. The authority pointed out that the VAT Act expressly specifies the elements that a corrective invoice must contain and that, in the case of structured invoices, these data must be submitted in accordance with the applicable KSeF logical structure. Consequently, mandatory information concerning the corrected invoices should be included in the dedicated “DaneFaKorygowanej” section.
According to the tax authority, an attachment sent outside KSeF cannot be considered an integral part of a structured invoice. The authority emphasized that since the legislator provided for a specific method of transmitting data within the KSeF logical structure, information required by law cannot be replaced by a document functioning outside the system.
Since KSeF does not provide for the possibility of attaching such documents to invoices submitted to the system, information included exclusively in an external attachment cannot replace the elements required by the VAT Act. Therefore, the technical limitations of the system do not justify departing from the requirements concerning the content of a structured invoice.
The ruling demonstrates that tax authorities take a formal approach to the obligations associated with issuing invoices through KSeF. Even where difficulties result solely from the system’s technical limitations, this does not mean that mandatory invoice elements can be replaced by an external attachment sent outside KSeF.
The ruling may be particularly important for taxpayers conducting large-scale business activities and issuing collective corrective invoices covering thousands of documents. It indicates that, in the view of the tax authority, the requirements arising from the VAT Act and the KSeF logical structure take precedence over the technical limitations of the system itself. In practice, this means that taxpayers cannot replace mandatory invoice elements with alternative organizational solutions, even where those solutions are necessitated solely by KSeF’s functional limitations.