KSeF Kit
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Quick start

Here's what success looks like: a Stripe invoice finalizes, we file it to KSeF, and you get back a UPO and a KSeF number — written straight onto the Stripe invoice. Automatically, with no action from you.

KSeF Kit gets you there in three steps; your first test invoice takes a minute.

1. Install the Stripe App

In your Stripe Dashboard, open Apps → App Marketplace, search for KSeF Kit, and click Install. This is the cloud edition — you host nothing. Installing provisions an account and an active Stripe link; from then on every finalized invoice reaches us by webhook (we wire that webhook for you — no manual setup in Stripe Developers).

Prefer to run it yourself? See Self-hosting.

2. Onboarding (3 steps)

After installing, open the app from Stripe → Apps → KSeF Kit (or sign in to the app directly). A wizard walks you through three steps — the next incomplete step opens itself.

  1. Stripe — the link is created when you install the app.
  2. Company profile — enter your NIP. We validate the checksum and pull your name and address from the registry (MF Biała lista / GUS). These become the seller details on the invoice.
  3. Connect KSeF — the TEST environment first (preselected), then paste your token. Details: Connecting KSeF.

You can skip the KSeF step — invoices then wait safely in the queue and are not filed until you connect.

3. First test invoice

Once KSeF is connected to TEST we trigger the "aha" moment: we file a sample invoice through the normal pipeline against the sandbox. When the UPO comes back, you know it works — before your first real invoice arrives.

The UPO (official receipt) is the signed document KSeF returns once it accepts an invoice — together with the KSeF number it assigns. It's your legal proof the invoice was filed. We keep it with every accepted invoice.

All of this happens in the TEST environment (a sandbox) — with no legal effect. Test freely. See Data & security.

Important — we never file a sample invoice into PRODUCTION. A fictitious document in the national registry would breach the law (art. 108 VAT). On a production-connected account with nothing yet to file you see a calm "You're live" state, and your first real Stripe invoice files automatically. To rehearse, switch to TEST first.

Next

KSeF is mandatory from 1 January 2027. Worth being ready early — the in-app readiness checklist walks you through it.