KSeF 2026: what changes in B2B sales and how to prepare

KSeF, Poland's National e-Invoicing System, is already mandatory: the largest companies have issued invoices through it since 1 February 2026, all other VAT taxpayers since 1 April 2026, and every business has had to receive invoices through KSeF since 1 February. In B2B sales this means the invoice is an XML file accepted by the Ministry of Finance system, not a PDF sent by email. One more date is still ahead: on 1 January 2027 the transition period ends, penalties apply and the KSeF number becomes part of bank transfers. This article covers what has already changed in day-to-day sales and what to sort out before the end of the year.

What KSeF is and who the obligation covers

KSeF is a central Ministry of Finance platform through which companies issue and receive structured invoices. A structured invoice is an invoice in the XML format defined by the Ministry, whose issue is confirmed by the assignment of a KSeF number. The seller doesn't "send" it to the counterparty; the seller uploads it to the system, and the buyer retrieves it from that same system.

The obligation comes from the Act of 16 June 2023 amending the VAT Act (Journal of Laws 2023, item 1598), in the final form set by the Act of 5 August 2025 (Journal of Laws 2025, item 1203). It covers invoices between businesses. According to ksef.podatki.gov.pl, the exclusions include invoices for private individuals not running a business (these can be issued in KSeF voluntarily), entities with no registered office or fixed establishment in Poland, and invoices under the OSS and IOSS schemes.

KSeF deadlines: what already applies and what arrives in 2027

The schedule set by the Act of 5 August 2025 has three dates. Two have already passed, and the transition period runs until 31 December 2026. Status as of September 2026, based on the Ministry's page Legal basis and key dates:

The PLN 10,000 limit applies to the total value of sales documented with invoices in a given month, not to a single invoice. If you rely on it, keep an eye on the running total, because once it is exceeded, invoices have to be issued in KSeF.

What changes in day-to-day B2B sales

Issue date and receipt date

The issue date of a KSeF invoice is the date entered in field P_1 of the XML file. In normal online mode this is the day you upload the invoice to the system. If you upload it later than the P_1 date, the invoice is treated as issued in offline24 mode and must reach KSeF no later than the next business day. The buyer receives the invoice the moment KSeF assigns its number, whether or not they have downloaded it. That date also starts the buyer's right to deduct VAT.

The practical consequence: an invoice created "some time later" in a different program from the order easily falls outside these limits. The closer to the order the document is created, the fewer dates someone has to watch by hand.

The invoice reaches the customer through the system, not the inbox

Your counterparty has the invoice in KSeF whether or not you email them anything. You can still send a PDF, but it is only a visualisation. The document the customer books is the file in KSeF. The same goes for corrections: a corrective invoice for a KSeF invoice is also a structured invoice.

A wrong tax ID puts the invoice in someone else's account

KSeF makes the invoice available to the buyer identified by the tax ID (NIP). A single wrong digit means the document goes to a different company and your customer never sees it. Customer details retyped from an email or a phone call are now a bigger risk than with PDF invoices, because the mistake leaves your company.

The KSeF number in payments

From 1 January 2027, a business paying for a KSeF invoice by bank transfer puts its KSeF number in the transfer title, or, when paying several invoices at once, the collective identifier assigned by the system. Lawmakers postponed this requirement to give banks and software vendors time to adapt. For the seller the takeaway is simple: the KSeF number has to be easy to find on the order, because that is what you will use to match payments to invoices.

Why a fragmented document flow hurts more under KSeF

Before KSeF, an invoice was a file you could fix before sending, and a mistake in the date or the buyer's details was cleared up by email. Now every invoice gets a number in a government system the moment it is uploaded. If the order sits in the store, the invoice in the accounting program and the payment on the bank statement, each of those three channels has its own data and its own dates.

Most of the trouble with KSeF doesn't come from the system itself, but from a fragmented flow: the order in one place, the invoice in another, the payment in a third. Anyone who has this connected experiences the obligation as a formality.

Connecting these channels means one source of customer data, invoice lines copied from the order by the system rather than by a person, and the KSeF number stored on the same order the payment will arrive for.

How to prepare B2B sales before 2027

1. Check whether you use transition-period reliefs. If you still issue some invoices outside KSeF under the PLN 10,000 monthly limit, that option disappears in January 2027.
2. Issue all B2B invoices through software that supports KSeF. The software needs authorisation to issue invoices in KSeF on behalf of your company; its vendor explains how to grant it.
3. Stop retyping buyer details by hand. The tax ID and company details should come from the business register, not from an email.
4. Connect the order with the invoice. Line items, net prices and VAT rates should reach the document from the order, without copying.
5. Get ready for the KSeF number in transfers. Decide where your team sees an invoice's KSeF number and how it is matched with a payment.
6. Agree the rules for private customers and foreign buyers. These invoices follow different rules, so decide with your accountant whether they go to KSeF.

How vendispace connects the order with KSeF

vendispace is not accounting software and does not connect to KSeF directly. It connects the order with the program you already invoice in: inFakt or Fakturownia. A company has one active accounting connection, and we set up the integration once you share the access details.

• Lines from the order. The invoice is built from the same lines as the order: products with their net price and VAT rate, additional services, shipping, and a discount code split across VAT rates.
• When it is issued. You choose the order status at which the invoice is issued automatically, or you issue it with a button on the order screen.
• KSeF through the accounting program. Once you enable the KSeF option in the integration settings, the accounting program uploads the invoice to the system, and the status and KSeF number come back to the order. A background job running every 10 minutes finishes invoices still being created and fetches KSeF statuses.
• Customer details from GUS. For a Polish company, the name and address come from the GUS business register by tax ID, so nobody retypes them.
• PDF on the order. The invoice PDF is stored on the order, and the customer downloads it from the store.

The same order supports online payment or payment on deferred terms. The invoice, payment and shipment therefore describe one transaction. We cover this in more detail in the article on B2B integrations: invoices, payments and shipping.

Summary

• Since 1 April 2026, KSeF applies to practically every VAT taxpayer in B2B sales, and receiving invoices through the system has been mandatory since 1 February.
• The transition period ends on 31 December 2026. From 2027 penalties apply, the PLN 10,000 limit for invoices outside the system disappears, and a transfer for an invoice needs its KSeF number.
• The issue date is field P_1, and the receipt date is the moment the KSeF number is assigned. A late upload means offline24 mode and a deadline of the next business day.
• Manual retyping carries most of the risk: tax IDs, line items, dates. A flow in which the invoice is created from the order removes most of these errors.

Frequently asked questions

Do I have to issue invoices for private individuals in KSeF?

No. Invoices for individuals who don't run a business are excluded from the obligation and can be issued in KSeF voluntarily. A consumer receives the invoice in a way agreed with them, for example as a PDF. If one store serves both businesses and private customers, agree with your accountant which invoices go to the system.

Can I still send customers a PDF invoice?

Yes, but only as an informational copy. For a buyer that is a Polish company, the invoice is the document in KSeF, and it counts as received the moment the system assigns its number. Many accounting teams still ask for a PDF, because it is easier to read than an XML file.

What is the penalty for issuing an invoice outside KSeF?

Until 31 December 2026 there is none, because the penalty provisions (Art. 106ni of the VAT Act) apply from 1 January 2027. After that, an invoice issued outside the system when the obligation applies can lead to a financial penalty calculated from the VAT amount shown on the invoice. The transition period is a good time to find every invoice that is still created "on the side".

How do I correct an invoice issued in KSeF?

With a corrective invoice, also issued in KSeF. An invoice that has received a number in the system cannot be edited or deleted. In vendispace you issue the correction in your accounting program. You can adjust prices and quantities on an order until the customer has paid it, but do it before the invoice is issued, because changing the order does not correct a document that is already in KSeF.

What about a customer from abroad?

The obligation applies to the seller, so a Polish company covered by KSeF issues invoices for foreign counterparties in it too. Such a buyer usually doesn't use KSeF, so you deliver the invoice in an agreed way, most often as a PDF visualisation. Settle the details, especially the VAT rate and reverse charge, with your accountant.

Does vendispace send invoices to KSeF?

Not directly, only through the connected accounting program. With the KSeF option enabled, inFakt or Fakturownia uploads the invoice to the system, and the KSeF number appears on the order in the admin panel. KSeF authorisations and purchase invoices are still handled by your accounting program.

The invoice is the last step of an order, so what happens before it matters too: the net prices the invoice lines are built from and the individual price list for each customer. You can see what each plan includes on the pricing page. Create a free account and test the whole flow, from order to KSeF number, with one customer.