KSeF e-invoices for Shopify stores in Poland

From 2026, KSeF e-invoicing has changed how invoices are issued in Poland, and sending PDF invoices by email will no longer be enough.

Instead, invoices will need to be issued as structured electronic documents and submitted through a government system called KSeF.

This affects how invoices are issued, when they become legally valid, and which invoicing systems businesses can use.

Below, you’ll find out whether KSeF applies to your business, what changes in practice, and how to prepare your invoicing setup in your Shopify store.

In this article, we will discuss:

• What is KSeF e-invoicing in Poland?
• What does a KSeF e-invoice format look like?
• When does KSeF e-invoicing become mandatory in Poland?
• How does Polish e-invoicing apply to Shopify stores selling B2B?
• Support for Polish KSeF e-invoices in Sufio
• Frequently asked questions

KSeF (Krajowy System e-Faktur) is Poland’s national system for issuing structured electronic invoices, managed by the Polish Ministry of Finance.

From 2026, KSeF is mandatory for VAT taxpayers based in Poland for invoices covered by Polish VAT rules.

While PDF invoices may still be shared for convenience, they will only serve as a visual representation of the invoice.

The legally valid invoice is the structured electronic invoice that is submitted to and accepted by KSeF.

For B2B transactions, an invoice is considered legally issued only once KSeF validates and accepts it. This affects the legal issue date of invoices, VAT reporting, and accounting workflows.

Some transactions are outside the scope of this obligation. For example, invoices for consumers (B2C) may be issued in KSeF, but this remains voluntary even after February 1, 2026.

A KSeF e-invoice may look familiar to you and your customer, but how it is issued is different.

The invoice itself is issued as a structured XML file that follows the official FA(3) format defined by the Polish tax authority.

This structured format contains all invoice data in a machine-readable form and allows KSeF to automatically validate the invoice data before accepting it.

Once accepted, the e-invoice:

• Receives a unique KSeF number
• Becomes legally valid for tax purposes
• Is archived by the tax authority for ten years

Because of this, invoice data must be complete and accurate at the moment of submission.

KSeF is being introduced in phases.

The timing of the obligation depends on a business’s turnover, not on its industry or invoicing software. The main deadlines are:

Under the KSeF regime, the basic VAT refund deadline is reduced from 60 days to 40 days starting February 1, 2026.

As a Shopify store, you need to ensure that your invoicing process supports KSeF e-invoices for your Polish B2B customers.

Polish Shopify stores selling to business customers should:

1. Collect the necessary information to determine whether a sale falls under the Polish B2B e-invoicing obligation, such as the customer’s Polish VAT number and billing address.
2. Generate invoices from qualifying orders in the structured KSeF-compatible XML format.
3. Submit invoices to KSeF so they can be validated and made available to the customer.

PDF invoices can still be emailed or made available for download, but they do not replace the structured KSeF e-invoice submitted for Polish B2B sales.

For Shopify stores affected by KSeF, Sufio will help merchants adapt their invoicing process to the Polish e-invoicing requirements.

Sufio will automatically create the structured invoice data required for KSeF, help reduce issues related to missing or incorrect invoice information, and submit invoices to the KSeF system on your behalf.

KSeF e-invoices will be generated for invoices and credit notes issued to Polish business customers (B2B).

This applies to both invoices automatically created from orders in your Shopify store as well as invoices created manually in the Sufio app.

The same applies to credit notes, whether they are automatically created from refunds and returns in your online store or created manually in the app.

At the same time, the app will continue to generate professional PDF invoices that can be emailed to your customers or downloaded from their accounts in your online store.

This allows you to maintain a familiar invoicing workflow while preparing for mandatory e-invoicing in Poland.

What is the KSeF number on an invoice?

The KSeF number is a unique reference number assigned to an invoice or a credit note once it is accepted by KSeF.

It confirms that the document has been successfully submitted through KSeF and is legally valid for tax purposes.

The number is generated automatically and can be used to identify the invoice in accounting records, audits, and payments.

What is the KSeF document number?

The KSeF document number refers to the same identifier as the KSeF number.

It is the official reference assigned by KSeF to each accepted invoice or credit note. In practice, both terms are used interchangeably to refer to the unique number that confirms successful submission and validation in KSeF.

How does KSeF improve tax compliance?

KSeF helps improve tax compliance by giving tax authorities direct access to invoice data as invoices are issued.

Because invoices are validated before they are issued, errors and inconsistencies can be detected earlier.

This reduces the risk of incorrect VAT reporting, limits fraud, and simplifies tax audits for both businesses and authorities.

What are KSeF requirements?

To comply with KSeF, businesses must:

1. Issue B2B invoices in the official structured XML format FA(3)
2. Submit invoices to KSeF for validation
3. Ensure invoices are accepted by KSeF before they are considered legally issued
4. Store and reference the assigned KSeF number

These requirements apply to VAT-registered businesses in Poland from their applicable KSeF start date in 2026, depending on their turnover.