KSeF FAQ: Who Must Use It, When, and How to Get Ready

Poland's KSeF system generates a lot of questions — and a lot of confusing answers. Here are the most common ones, answered as clearly as possible.

What is KSeF?

KSeF (Krajowy System e-Faktur) is the Polish government's centralised electronic invoicing system, operated by the Ministry of Finance. Instead of sending PDF invoices by email, businesses must submit structured XML invoices directly to the government platform, which assigns each one an official reference number.

When does it become mandatory?

April 1, 2026 for active VAT payers issuing B2B invoices in Poland.

The original January 2024 deadline was delayed after technical issues were identified during testing. The April 2026 date is considered firm by the Ministry of Finance.

Who must use KSeF?

Any business that:

Is registered as a VAT payer in Poland
Issues invoices to other businesses (B2B transactions)
Has a registered business address in Poland or a Polish tax number (NIP)

Are there any exemptions?

Yes, some transactions are currently excluded from mandatory KSeF:

B2C invoices (to individual consumers) — not required via KSeF, though it can be used optionally
Invoices issued by foreign businesses without Polish establishment or VAT registration
Some simplified invoices below certain thresholds (rules still being finalised)
Transactions within special economic zones — specific exemptions apply

If you're unsure whether your business falls under an exemption, consult a Polish tax advisor. The rules are detailed and enforcement is strict.

What format does KSeF require?

KSeF invoices must be submitted as XML files conforming to the FA(3) schema (Faktura structured format, version 3). This is a technically precise format requiring:

Correct NIP numbers for both parties (verified against the White List)
Specific field names and data types as defined by the Ministry
AES-256 encryption and SHA-256 digital signature
Direct API submission — not email or file upload

Can I still send PDF invoices?

Not for B2B transactions after April 1, 2026. Your PDF can be a supplementary document, but the legally valid invoice is the KSeF XML with its reference number. Clients will increasingly refuse to accept invoices without a KSeF number as it becomes their only way to legally deduct input VAT.

What if I miss the deadline?

The penalties are serious:

Up to 100% of the VAT amount on invoices issued outside KSeF
Administrative penalties for systematic non-compliance
Risk of your invoices being rejected by clients who need the KSeF reference number for their own tax compliance

Do I need to keep paper or PDF copies?

Once an invoice has a KSeF reference number, it is stored in the government system for 10 years. You are not required to maintain separate archives for KSeF invoices, though most businesses keep local copies for practical reasons.

Can I use my existing accounting software?

Only if your software has been updated with a certified KSeF integration. Contact your software vendor to confirm:

Does the software generate valid FA(3) XML?
Does it submit directly to the KSeF API (not just export files)?
Has it been tested against the KSeF production environment?

Major platforms (Comarch ERP, Symfonia, Subiekt GT) are releasing updates. Check that yours is certified.

What if I have a custom or legacy system?

You have two main options:

Use a standalone KSeF tool alongside your existing system — tools like FakturAI let you create and submit KSeF invoices independently, even if your accounting software isn't integrated
Custom API integration — connect your existing system directly to the KSeF API via middleware. This is more complex but keeps your workflow unified. Raeolas.AI specialises in these custom integrations for businesses using SAP, Comarch, or proprietary systems

How do I test before the deadline?

The KSeF sandbox environment is available at ksef-test.mf.gov.pl. Testing your solution against the sandbox before going live is strongly recommended — it catches formatting errors, authentication issues, and edge cases before they become live submission failures.

Is there a free way to get started?

Yes. FakturAI offers a free Solo plan with 20 invoices/month — no credit card required. For most freelancers and small businesses, this covers everything needed for KSeF compliance at no cost.

Quick Checklist

Confirm whether your business falls under the April 1, 2026 mandate
Check if your current invoicing software has a certified KSeF integration
Test your solution in the KSeF sandbox environment
Issue your first test invoice before March 31
Inform your clients and accounting team of the change

The deadline is real. Start now.

Raeolas.AI helps businesses across Poland and Europe integrate with KSeF and automate their financial workflows. Book a free call to discuss your setup.