Before you click "Send": what you need
Issuing an invoice in KSeF takes three things, none of which costs more than a few minutes.
Software connected to KSeF. This can be the free Taxpayer Application (Aplikacja Podatnika KSeF) from the Ministry of Finance, or a commercial tool that walks you through it (like Biurko). You create invoices in the software; it talks to KSeF for you.
An authentication method. KSeF needs to know it's really you. Your options are Profil Zaufany (Poland's Trusted Profile e-ID), a qualified electronic signature, or a KSeF certificate. Tokens still work too, but only through the end of 2026.
A NIP — yours and your buyer's. The NIP is the Polish tax identification number. Most software pulls the rest of the company details automatically from the GUS (Central Statistical Office) registry once you type it in.
If you're still choosing how to log in, go with a KSeF certificate. Unlike a token, it doesn't disappear at the end of 2026, and after a one-time setup your software signs in to KSeF automatically. (More in our guide to KSeF authentication — replace link before publishing.)
Step by step: your first invoice
Here's the full path using Biurko. In any other program the steps look similar — only the screen layout changes.
Create an account and add your company. You enter your NIP and the address details load from GUS. This is a one-time step — for later invoices your company is already in the system.
Connect to KSeF. You point to your certificate (or sign in with Profil Zaufany) and authorize access. Also done once.
Create the invoice. Enter the buyer's NIP (details load automatically again), add line items — name, quantity, price, VAT rate — and set a payment due date. These are the same fields you'd fill on any invoice.
Click "Send to KSeF." The software converts your invoice into an XML file in the FA(3) structure and sends it to the system. You don't need to know anything about XML — it happens under the hood.
Wait for acceptance. This usually takes around two minutes. KSeF checks the invoice against the schema and, if everything is in order, assigns it a KSeF number.
Download the UPO. This is the official confirmation that your invoice reached the system. Save it — it's your proof of issuance.
That's it. Once the KSeF number is assigned, the invoice counts as issued and delivered. You don't need to email it — your buyer already has it inside KSeF. You can send a PDF for convenience, but formally it's the same document.
What you get after sending: the KSeF number and UPO
Two things worth understanding, because they come up with every invoice:
The KSeF number is a unique identifier assigned by the system. From the moment it's issued, the invoice officially exists — before that, it's only a draft. It's also what determines when your buyer can deduct VAT.
The UPO (urzędowe poświadczenie odbioru, official receipt confirmation) is a system-stamped acknowledgment. Think of it as a registered-mail return receipt — black-and-white proof the document arrived. Good software downloads it automatically and attaches it to the invoice.
And if an invoice is rejected? The usual causes are a wrong buyer NIP or a duplicate. Raw KSeF returns a code — something like 21115 — that means nothing on its own. Good software turns it into a concrete message, for example: "the buyer's NIP isn't registered as an active VAT payer — fix it and resend." You correct one field and click again.
Common first-invoice slip-ups
A consumer (B2C) invoice doesn't go to KSeF. Sales to private individuals are documented the old way — a receipt or an invoice outside the system. KSeF is for B2B.
The buyer's NIP has to match. If your contractor gave the wrong number or isn't an active VAT payer, the invoice won't go through. It's worth verifying the NIP before sending.
You can't edit a KSeF invoice after sending. There's no edit button — you fix a mistake with a correcting invoice (faktura korygująca), which also goes to KSeF. So check your line items before clicking "Send."
The PLN 10,000 threshold is not an exemption. If you're relying on the transitional period, remember: it's a conditional break that disappears the month you first exceed it — and doesn't come back. (We unpack this in a separate article — replace link.)
Checklist: your first KSeF invoice
I have software connected to KSeF (Ministry of Finance or commercial)
I've chosen a login method — ideally a KSeF certificate
I've added my company (NIP → details from GUS)
I have a correct buyer NIP (verified, ideally)
I've checked line items and VAT rates before sending
After acceptance, I downloaded the KSeF number and UPO
I know corrections are made with a correcting invoice, not by editing
Wrapping up
A first KSeF invoice only looks intimidating from a distance. In practice it's a few fields, one click, and a short wait for a KSeF number. The one-time setup takes the most time — issuing each invoice after that is a matter of seconds.
Biurko walks you through the whole path: certificate login, automatic GUS lookups, and readable messages instead of raw error codes. Try it free for 14 days at biurko.io and issue your first e-invoice today.
FAQ
How do I issue my first invoice in KSeF? Create an account in software connected to KSeF, add your company by NIP, authenticate (for example with a KSeF certificate), fill in the buyer's details and line items, then click "Send to KSeF." The system assigns a KSeF number, and you download the UPO as proof of issuance.
Do I need a certificate to issue an invoice in KSeF? Not necessarily — you can also use Profil Zaufany or a qualified electronic signature. Tokens work through the end of 2026. A KSeF certificate is the most convenient option for ongoing use, though, because it doesn't expire at year-end and lets your software sign in automatically.
How long does it take to send an invoice to KSeF? Filling in and sending takes a few minutes. After you click "Send," KSeF usually accepts the invoice in about two minutes and assigns a number. The first time takes a little longer because of the one-time account and login setup.
What is a UPO in KSeF? A UPO (urzędowe poświadczenie odbioru, official receipt confirmation) is acknowledgment from KSeF that your invoice was accepted. It works like an electronic return receipt — proof the document reached the system. Save it; good software downloads the UPO automatically.
Can a KSeF invoice be corrected after sending? No. An invoice accepted by KSeF can't be edited. Any change is made with a correcting invoice, which is also sent to KSeF. That's why it's worth double-checking the buyer, line items, and VAT rates before clicking "Send."