How to Issue Your First Invoice in KSeF — Step by Step

Introduction: What is KSeF and Why is it Mandatory?

The Krajowy System e-Faktur (KSeF) is an electronic invoice registration system introduced by Poland's Ministry of Finance. As of April 1, 2026, every VAT taxpayer in Poland must issue invoices electronically through this system.

KSeF aims to eliminate the gray economy and VAT fraud. Invoices are stored centrally with the tax authorities, accessible to both transacting parties, and taxpayers receive confirmation of submission (UPO).

In this article, we'll show you exactly how to issue your first invoice in KSeF without errors or complications.

Preparation: Requirements Before Sending Your Invoice

Before you send your first invoice, you need to prepare several things. Here's a complete checklist.

1. Trusted Profile or e-Signature

To access KSeF, you must have:

• Trusted Profile – free option, popular for most companies
• e-Signature – certified electronic signature (more expensive but more universal)
• UPO Certificate – if you use software integrated with KSeF

If you don't have a trusted profile yet, register at https://login.gov.pl. The process takes just a few minutes.

2. Confirmation of VAT Activity

The tax office must confirm you are an active VAT taxpayer. Check your status:

• On the https://ksef.podatki.gov.pl official KSeF portal
• In the Central Register of Taxpayers (CEiR) – check your own and your contractors' status

3. Seller and Buyer Data

Prepare:

• Your company name, NIP (tax ID), business address
• For each buyer: name, NIP (if a Polish company), address, and optionally bank account number
• Transaction identifiers (order numbers, contract numbers)
• Product/service information (descriptions, codes, units of measure)

Step 1: Choose Your Invoicing Tool

You have two main options – each with advantages and disadvantages.

Option A: KSeF Taxpayer Application (Free)

Application available at https://ksef.podatki.gov.pl – the official tax authority tool.

• Advantages: Free, secure, supported by Ministry of Finance
• Disadvantages: Slower, limited features, manual invoice entry

Ideal for companies issuing a few invoices per month.

Option B: Invoicing Software Integrated with KSeF

Programs such as Fakturomania, iSeria, Enova, Sage – automate KSeF submission.

• Advantages: Fast, automatic submission, archive, reports, accounting integration
• Disadvantages: Subscription costs (€5–150/month), learning curve required

Recommended for companies with regular invoice flow (10+ per month).

Step 2: Log In to KSeF

If you chose the taxpayer application:

1. Go to https://ksef.podatki.gov.pl
2. Click "Login" and select "Trusted Profile"
3. Log in to login.gov.pl portal
4. Authorize KSeF to access your data
5. Wait for activation confirmation (usually a few minutes)

If you use invoicing software – log in with credentials integrated with KSeF.

Step 3: Prepare Invoice Data

Every invoice in KSeF must contain precisely defined information in the correct structure.

Mandatory invoice elements:

Invoice Element	Description / Requirements
Issue Date	Date cannot be in the future (system will reject it)
Invoice Number	Unique in your organization, sequential numbering (e.g., INV/2026/001)
Seller Data	Company name, NIP, full business address (street, house number, zip, city)
Buyer Data	Name, NIP (for Polish companies), address, zip code, city
Product/Service Descriptions	Precise descriptions (e.g., "IT consulting service – 8 hours work")
Quantities and Units	Number, unit of measure (pcs., hrs., kg)
Unit Price (Gross/Net)	Must match accounting records
VAT Rate	Standard 23%, reduced 8%, zero 0%, or exempt (with reason)
Total Amount (Net, VAT, Gross)	Must be calculated correctly
Currency	Usually PLN; for foreign transactions, indicate currency code and exchange rate

Step 4: Submit the Invoice to KSeF

In the KSeF application:

1. Click "New Invoice" and fill in all required fields (see table above)
2. Generate XML format (system does this automatically)
3. Review all details – check for typos, especially NIP numbers
4. Click "Submit to KSeF"

In third-party software:

1. Create invoice in the normal way
2. Select "Export to KSeF" or "Send to KSeF"
3. Software automatically submits the XML to the system

Step 5: UPO Confirmation and Archiving

After submission, KSeF returns an UPO (Urzędowe Potwierdzenie Odbioru) – Official Confirmation of Receipt.

What does UPO contain?

• UPO number (unique identifier)
• Invoice number and date
• Timestamp of KSeF receipt
• Submission status (accepted/rejected)

Keep the UPO! It's proof that your invoice was registered in the system. Store it with your invoice in your accounting archive.

Common Errors and How to Avoid Them

Even experienced accountants make mistakes when issuing their first invoices in KSeF. Here are the most common ones:

1. Incorrect NIP Format

Problem: KSeF rejects invoices with missing leading zeros or incorrect NIP formatting.

Solution: Always include the full 10-digit NIP (e.g., 1234567890, not 123456789).

2. Mismatch Between Invoice and Buyer Data

Problem: Company name doesn't match business address, or registered NIP doesn't match the company.

Solution: Verify buyer data in CEiR before issuing the invoice.

3. Future Invoice Date

Problem: System rejects invoices dated in the future.

Solution: Always use today's date or an earlier date (invoices can be issued up to 14 days after the transaction).

4. Incorrect VAT Rate

Problem: Wrong VAT rate doesn't match the type of transaction (e.g., goods vs. services).

Solution: Consult tax rules for your specific transaction type. Check if GTU (Group Tax Code) designation is required.

5. No Invoice for Foreign Buyer Without NIP

Problem: For foreign buyers or those without a Polish NIP, the field remains empty, causing validation errors.

Solution: Leave the NIP field empty, but always fill in the full address.

FAQ – Your Questions Answered

Q: Does every VAT taxpayer have to use KSeF?

A: Yes, as of April 1, 2026, all VAT taxpayers in Poland must issue invoices through KSeF. The only exceptions are companies not registered for VAT (business ID holders only).

Q: What is UPO in KSeF?

A: UPO is Official Confirmation of Receipt – a formal document issued by KSeF after correctly receiving your invoice. It proves your invoice was registered in the system.

Q: Can I send invoices in PDF or only XML?

A: KSeF requires invoices in XML or UBL format (structured data). PDF is only a visualization format – the system generates it automatically from the XML structure.

Q: What is a Trusted Profile and do I need one?

A: A Trusted Profile is a secure way to authenticate yourself in government systems. Every VAT taxpayer wanting to send invoices through KSeF must have a Trusted Profile or e-Signature.

Q: What information must appear on a KSeF invoice?

A: Invoices must include: issue date, document number, seller and buyer data (with NIP), product/service descriptions, quantities, prices, VAT rates, currencies, and if required – GTU markings and reverse charge procedures.

Q: Can I issue a corrective invoice in KSeF?

A: Yes, corrective invoices (credit notes) are sent to KSeF like regular invoices, but marked as corrective documents with reference to the original invoice.