KSeF and Invoices: What Counts as B2B, Export, and Foreign Buyers

KSeF (Krajowy System e-Faktur) is often summed up as "from February 2026 everything has to go through KSeF". That is imprecise. KSeF covers a specific slice of invoicing — B2B between Polish VAT payers. Outside that slice, different rules apply, and that is exactly where integration errors creep in. Here is the split you need to know before you start integrating.

What Falls Under KSeF: Domestic B2B

The core of the obligation is simple: domestic B2B invoices of Polish VAT payers issued under the Polish VAT Act. If you are established in Poland or you are a Polish VAT payer and you invoice another VAT payer, you issue a structured e-invoice through KSeF.

The rollout is phased:

• From 1 February 2026, issuing is mandatory for large VAT payers — those with 2024 turnover above PLN 200 million (roughly 4,200 entities). The threshold is calculated from the previous year.
• From 1 April 2026, issuing is mandatory for all other VAT payers, except micro-businesses.
• Micro-businesses (the smallest VAT payers) are obliged only from 1 January 2027.

On top of that there is a transitional relief: a VAT payer whose monthly value of invoices issued outside KSeF does not exceed PLN 10,000 gross may invoice outside KSeF until 31 December 2026. The obligation catches up with them on the invoice that crosses that limit. So the common "from April 2026 everyone is in" is a simplification — micro-businesses and the under-PLN-10,000-per-month group come in only in 2027.

Receiving Invoices: Mandatory for Everyone Before Issuing

This is easy to miss. All VAT payers must receive invoices through KSeF from 1 February 2026 — even those who do not yet issue in KSeF themselves.

For integration this means two things. The receiving side has to be ready before the sending side. And you cannot wait until your own issuing obligation catches up with you — you need the protocol for downloading and processing incoming structured invoices from February 2026, regardless of how large your company is.

Foreign Buyer: The Invoice Goes Into KSeF, the Document Goes Out

A common question: I sell abroad, does KSeF apply to me? Yes.

An invoice issued to a foreign buyer is issued in KSeF, because it is an invoice under Polish regulations. The fact that the buyer sits in Germany or the US changes nothing about the obligation to issue it in KSeF.

The difference is in how you deliver the document. The foreign buyer has no access to KSeF, so they receive the invoice outside the system — typically as a PDF visualisation or a shared link to it. The structured invoice stays in KSeF as the official record; you send the buyer a readable form.

From an integration standpoint, this means two output paths from one source: structured XML into KSeF, and a human-readable visualisation (PDF or link) to the buyer. Both have to match the same invoice.

What Does Not Fall Under KSeF

Knowing what not to send is as important as knowing what to send. Two main categories:

B2C invoices to end consumers. There is no structured-invoice obligation toward a consumer in the sense KSeF handles it for B2B. If your application also invoices end customers, those documents do not belong in KSeF and you have to separate them in your logic.

Purchase invoices from foreign suppliers. When you buy from a supplier established outside Poland, you do not record their invoice through KSeF. The foreign supplier does not have to enter it into KSeF — companies selling to Polish entities from abroad are not obliged to use Polish structured e-invoices. KSeF is not used to report such a purchase.

The practical consequence for integration: your routing logic has to classify every document. Domestic B2B → KSeF. B2C → outside KSeF. Incoming from a foreign supplier → outside KSeF. Mixing these categories up is a silent error — either you send the government system something that does not belong there, or you fail to send something that does.

Attachments: Yes, but With Prior Notification

From 1 February 2026 it is possible to issue an invoice in KSeF with an attachment. It is not automatic, though. It requires prior notification of the intent to issue and transmit invoices with attachments, submitted through e-Urząd Skarbowy (can be filed from 1 January 2026).

The workflow detail is worth verifying against the currently published FA(3) schema before you start implementing — there are more moving parts here and the schema is still being tuned. If your process needs attachments, count on it being not just an extra field in the XML but a separate registration step with the tax office.

What to Take Away for the Integration

To sum it up from the standpoint of the person writing that integration:

• Routing is the first decision. Before you deal with sending, you have to be able to classify every document (domestic B2B / B2C / foreign buyer / incoming from abroad). The wrong classification is a silent error.
• Receiving before issuing. Receiving through KSeF is mandatory from February 2026 for everyone. Do not underestimate this side.
• Export = two output paths. XML into KSeF, a readable visualisation to the buyer. From one source, onto the same invoice.
• Attachments have their own registration. Without prior notification through e-US, you cannot issue them.

And above all of it stands what we wrote earlier: every submission to KSeF has to be durable and idempotent — asynchronous submit, status polling, UPO confirmation. Routing decides what to send. A robust pipeline makes sure it does not get lost on the way.

FAQ

Does an export invoice to a foreign buyer have to go through KSeF?

Yes. If it is an invoice under Polish regulations, it is issued in KSeF even for a foreign buyer. The buyer receives it outside KSeF, though — typically as a PDF visualisation or a shared link, because they have no access to KSeF.

Do invoices from foreign suppliers fall under KSeF?

No. A purchase invoice from a supplier established outside Poland is not recorded through KSeF, and the foreign supplier does not have to enter it into KSeF. Foreign companies selling to Polish entities are not obliged to use Polish structured e-invoices.

Does KSeF apply to invoices to end customers (B2C)?

No. The structured e-invoice obligation through KSeF applies to B2B relationships between VAT payers. Invoices to end consumers (B2C) do not fall under this obligation.

We Build the Integration

We build KSeF integration in production — structured FA(3) invoices, routing by document category, asynchronous submission with confirmation. One integration runs over 40,000 documents with 100% delivery; during a forensic recovery of another system we restored 15,141 missing documents that a previous pipeline had silently lost.

If you are working out what falls under KSeF for you and what does not, or you want an integration that will not fall over in January 2027 — get in touch.