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

KSeF — the National e-Invoicing System — is no longer optional and is becoming mandatory. If you sell B2B, the structured invoice will soon be the only accepted form of document — no PDF emailed over, no paper. We've gathered in one place what really changes in your day-to-day sales and how to prepare without panic.

What KSeF is in practice

KSeF is a central platform run by the Ministry of Finance, through which you issue and receive invoices in a single, standardized XML format. In short: you no longer "send" an invoice to your counterparty — you issue it into the system, and the counterparty retrieves it from that same system. Every document is assigned an official identifying number (a KSeF number) and an acceptance date.

For you as a seller, this means three things: an end to sending invoices manually, a single document flow instead of several channels, and full format compliance with the tax authority's requirements.

Rollout schedule

The obligation comes into force in stages — depending on your sales volume. The table below is an approximate schedule from the Ministry of Finance; before you roll it out, verify the current dates on the Ministry's website, as the deadlines have been pushed back in the past.

What changes for B2B sales

1. The issue date is the date KSeF accepts it

An invoice is considered issued the moment the system accepts it. This settles disputes over "when the document was actually issued," but it requires your ordering and invoicing processes to be connected — not run in two separate tools between which you retype data.

2. The KSeF number with payment

The number identifying an invoice in the system starts to accompany payments. The sooner your order → invoice → payment flow works as a single whole, the less manual reconciliation work there is.

3. No invoices "outside the system"

You'll no longer send a counterparty a PDF instead of a structured invoice. That's why the tool you sell in has to be able to issue the document directly into KSeF — ideally through an integration with the accounting software you already use.

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 will experience the rollout as a formality.

How to prepare, step by step

1. Check your deadline — determine which stage you fall into and when the obligation applies to you.
2. Make sure you invoice in line with KSeF — through inFakt or Fakturownia with KSeF support, not by hand.
3. Connect the order with the invoice — so the counterparty's details and line items reach the document without retyping.
4. Test the flow on a single counterparty before you switch over all your sales.

Where vendispace fits in

vendispace doesn't replace your accounting — it connects it to the order. The customer places an order in a store under your brand, and the invoice is created through your inFakt or Fakturownia account (with KSeF support). The counterparty's details are pulled from GUS by NIP, so you don't retype them, and online payment and a deferred term both work on the same document.

If you want to enter 2026 with a flow that's ready for KSeF, create a free account and test the entire process on a single order.