How to Issue an Invoice in KSeF in Poland — Step by Step 2026

Who must use KSeF?

From 2026, KSeF becomes mandatory for entrepreneurs according to the following schedule:

1. Large enterprises (>5 mln EUR revenue) — already mandatory
2. Medium and small companies — expansion phase
3. Micro-enterprises and sole proprietorships (JDG) — per the Ministry of Finance schedule

Even if you are not yet covered by the obligation, it is worth starting to use KSeF voluntarily — to prepare your systems and processes.

Step 1: Get access to KSeF

Login via Trusted Profile

1. Go to the KSeF website: ksef.mf.gov.pl
2. Select "Login" → "Trusted Profile / e-ID"
3. Redirect to login.gov.pl
4. Log in with your trusted profile credentials
5. Return to KSeF

Login via qualified signature

1. Plug in your qualified token (e.g. Certum, KIR)
2. Select "Login" → "Qualified signature"
3. Select the certificate
4. Enter your PIN

KSeF token (for API)

If you use accounting software (e.g. Oxyok), you do not need to log in manually. The program uses a KSeF authorization token:

1. Generate a token in the KSeF panel
2. Pass the token to your accountant or software
3. The program automatically sends invoices

Step 2: Create an invoice

Through the KSeF interface (manually)

1. In the KSeF panel, select "Generate invoice"
2. Fill in the invoice structure (XML form)
3. Enter the buyer's data (NIP (tax identification number), name, address)
4. Add line items (name, quantity, net price, VAT rate)
5. The system automatically calculates VAT and gross amounts
6. Send to KSeF

Through accounting software

Most sole proprietorships (JDG) will not issue invoices in the KSeF panel. Instead, the accounting software (Oxyok, inFakt, iFirma) generates the invoice and sends it to KSeF automatically:

1. Issue an invoice in the accounting software as usual
2. The program automatically converts the invoice to the KSeF structure (XML FA)
3. The program sends the invoice to KSeF via API
4. KSeF returns the KSeF number
5. The invoice is officially issued

FA invoice structure

An invoice in KSeF has a defined structure (the so-called FA(logical) structure). It must contain:

• Seller entity — NIP (tax identification number), name, address, "JDG" designation
• Buyer entity — NIP (tax identification number), name, address
• Invoice line items — each item separately: name, PKWiU (Polish classification of goods and services) (if required), quantity, unit, net price, VAT rate
• Summary — net amounts by VAT rate, VAT, gross
• Payment — due date, form (transfer/cash), bank account
• Additional information — order number, contract, annotations

Step 3: Check the invoice status

After sending the invoice to KSeF, the system assigns it a status:

1. Accepted — the invoice passed validation and is visible in the system. You receive a KSeF number.
2. Rejected — validation error (missing field, wrong NIP, invalid structure). You must correct and resend.
3. In progress — the invoice is awaiting processing

A KSeF number looks like this, for example: KSeF-2026-07-26-1234567890-123456-1-1

Step 4: Receive a cost invoice

KSeF works both ways — you not only send but also receive:

1. When a supplier issues you a cost invoice in KSeF
2. It automatically appears in your KSeF panel
3. Your accounting software retrieves it via API
4. You do not need to send the cost invoice to your accountant — the system does it for you

This is the biggest advantage of KSeF: automation on the cost side. Every invoice arrives instantly, without scanning and forwarding.

Most common mistakes when issuing

1. Wrong buyer NIP

If you enter a wrong NIP, KSeF will reject the invoice. Check the NIP before sending — you can do this on the VAT taxpayer whitelist.

2. Missing required fields

Every line item must have a specified VAT rate. You cannot leave the "rate" field empty. If the service is exempt — select "zw".

3. Inconsistent amounts

The sum of line items must match the final amount. If there is a difference of even 1 grosz, KSeF will reject the invoice.

4. Wrong currency

An invoice can be issued in PLN or foreign currency. If you choose foreign currency, you must provide the exchange rate and convert to PLN.

Pitfalls

1. An invoice without a KSeF number is invalid

Once fully implemented, an invoice WITHOUT a KSeF number is not valid for tax purposes. You cannot deduct it as a cost or deduct VAT from it. The KSeF number is proof that the invoice exists.

2. Correction deadline

A correction of an invoice in KSeF must be completed within a specified deadline. You cannot change a March invoice in November — the correction must be in the original settlement period or in accordance with art. 6 of the Accounting Act.

3. Global and simplified invoices

Global (collective) and simplified invoices have a simplified structure in KSeF, but they still must pass validation. Check whether your accounting software supports these types.

4. No internet

KSeF requires an internet connection. If you have no internet, you cannot issue an invoice. In practice: most accounting programs have an offline mode (they create the invoice locally and send it when the internet comes back).

FAQ

Do I need a qualified signature to use KSeF?

No. You can log in via Trusted Profile (free of charge). A qualified signature is only needed for specific operations (e.g. mass authorization).

What if KSeF is unavailable?

The Ministry of Finance anticipates emergency situations. Then invoices issued offline must be sent to KSeF within 2 business days of the system being restored.

Does an invoice in KSeF replace a paper one?

Yes. After KSeF is implemented, an electronic invoice in the system is the only valid form. Paper invoices and PDFs not sent through KSeF lose their tax validity.

Can I use KSeF through a mobile app?

The official Ministry of Finance KSeF app is available, but most sole proprietorships (JDG) will use accounting software that integrates KSeF automatically.

Need help with KSeF?

Oxyok accounting — from 49 zł + VAT per month. We integrate KSeF with your accounting, help you issue and receive invoices, and make sure everything works.

Write to: [email protected]

Disclaimer: The schedule for mandatory KSeF is determined by the Ministry of Finance and may change. This article is informational in nature — before making a decision, consult an accountant.