Retail & commerce · Poland · Tax compliance

Poland's KSeF rejects invoices over 1MB — every B2B file in FA(3) XML from April 2026.

On 1 April 2026 a Polish B2B invoice stopped being a piece of paper. For the corner shop, the trades firm with three vans, the marketing agency with a bookkeeper on retainer, the document is now FA(3) XML the Ministry of Finance must acknowledge through KSeF (Krajowy System e-Faktur, the state e-invoicing platform) before it legally exists. The Polish trade press logged what happened next: duplicates, rendering drift, an unfillable Podmiot3 (third-party billing) field, a 1MB ceiling, and a Profil Zaufany (national e-ID gateway) outage during pilot week.

01The pain

One megabyte. That is the ceiling on a Polish structured invoice, three megabytes if you attach scans, and a Warsaw wholesaler with a long line-item list finds out at the till that the document the buyer is waiting for will not fit. The schema is FA(3). The platform is KSeF (Krajowy System e-Faktur), run by the Ministry of Finance. From 1 April 2026, a B2B invoice that does not pass through it does not legally exist.²

1 April 2026. FA(3) XML only. 1MB ceiling. No KSeF, no invoice.

EY's tax alert sets the staging: large taxpayers with 2024 turnover above PLN 200 million (~€46m) from 1 February 2026, all other VAT-registered firms from 1 April, micro-entrepreneurs with monthly turnover under PLN 10,000 (~€2,300) from 1 January 2027. EY is blunt on what failure means: "a lack of ability to issue valid sales invoices." Not a fine. The right to bill at all. Once the platform went live, the Wolters Kluwer legal-tax title Prawo.pl catalogued the second-stage failures. Sellers issued the same invoice twice, once through KSeF and once on the side, and buyers booked it twice. Rendering drifted across tools, so a buyer's KSeF view stopped matching the seller's PDF. The Podmiot3 field, used for three-party and municipal billing, could not be completed in some invoicing software at all. During pilot week, Profil Zaufany — the national e-ID gateway and the only door into the system — went down.^1,2,3

"Obawa przed tym, że może wystąpić awaria paraliżująca codzienną pracę przedsiębiorców jest bardzo realna." ("The fear of an outage that paralyses everyday business is very real.") — Polish small-business advisory column, Infor.pl Księgowość, 2026

The Ministry of Finance has built a transitional period through the end of 2026 before formal penalties begin. Polish sole traders who hear "no penalties in 2026" think they have a year. They don't. From 2027 enforcement falls to the KAS (Krajowa Administracja Skarbowa, the national tax administration), and a sole-trader firm that skipped FA(3) integration loses the right to issue legally-valid B2B invoices. In a regime where the invoice does not exist until the state acknowledges it, downtime is not an inconvenience. It is a cashflow stop.^1,4

02Who solves this today

Polish-market vendors that publicly self-market to the KSeF niche on their own Polish-language homepage: invoicing platforms that name KSeF as a core feature, online-accounting services that make Krajowy System e-Faktur integration their headline, and ERP vendors who explicitly address the 1 April 2026 rollout. Each entry verified live and self-marketed in the niche on the date of writing. The list is intentionally narrow.

ifirma

Online accounting and invoicing for Polish sole traders. Homepage promise: "Pełna integracja z KSeF w każdym pakiecie." ("Full KSeF integration in every plan.") Books and invoices in one product.

ifirma.pl

inFakt

Polish invoicing-and-accounting service. Lead headline: "Połącz się z KSeF w minutę." ("Connect to KSeF in a minute.") Over a million invoices already filed through the platform from inFakt.

infakt.pl

Comarch

Polish ERP vendor. Dedicated KSeF page positions Comarch Betterfly, ERP Optima and ERP XL for SMBs. Free KSeF communication for ERP customers extended to 31 July 2026.

comarch.pl

Listed providers publicly market to the KSeF niche on their own Polish-language homepages. Inclusion is not endorsement. Adjacent Polish-market vendors were considered and excluded where their public pages either did not WebFetch cleanly or did not contain a verbatim KSeF self-marketing phrase on the homepage itself, per the Vietnam / US-AP precedent: two-or-three verified entries beat a longer list with a weak link. Trade-press outlets (Prawo.pl, Infor.pl), the international tax practice (Dudkowiak, EY) and the Ministry of Finance / KAS regulatory regime are cited above in section 01 as the source of the operator-side narrative, not as solution providers.

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