Poland KSeF e-invoicing – what gets validated?

This will fundamentally change how companies issue, validate, and exchange invoices. Unlike today’s systems where invoices are mostly an internal accounting artefact, KSeF introduces a central government platform that will validate invoices at the point of submission.

The answer to what’s actually validated by KSeF is a blend of technical validation, schema compliance, and content checks. Below we break down the most important rules, based on the official documentation and Ministry of Finance updates.

1. Compliance with the official XML schema?

• Every invoice must be submitted in XML format, encoded in UTF-8, and aligned with the official XSD schema published by the Ministry of Finance.

• KSeF verifies that all mandatory fields are present and properly filled in. Optional fields are not validated at this stage.

• If the XML does not match the schema, the invoice will be rejected immediately.

2. Unique invoice?

KSeF enforces strict duplicate detection to ensure every invoice in the system is unique. It checks the combination of:

1. Seller’s NIP (Subject1:NIP),

2. Invoice type (InvoiceType),

3. Invoice number (P_2 field).

If another invoice exists in KSeF with the same three parameters, it is flagged as a duplicate. The system applies this check over a 10-year horizon. Duplicate submissions return error code 440.

3. Checking the invoice date

• The invoice issue date (P_1 field) cannot be later than the date of receipt by KSeF.

• Future dates are not allowed. Past dates are technically accepted, but companies should still ensure compliance with accounting rules.

4. Exceeding batch and session limits?

KSeF imposes file size and batch restrictions:

• Individual invoices: up to 1 MB without attachments or 3 MB with attachments.

• Batch uploads: up to 50 ZIP files of 100 MB each per batch.

• Session limits: a maximum of 10 million invoices can be submitted in a single session.

5. Encrypted?

KSeF requires strict encryption standards:

• Invoice content is encrypted using AES-256-CBC.

• The symmetric encryption key is secured with RSAES-OAEP (SHA-256/MGF1).

• Metadata (hashes and sizes) of both raw and encrypted invoices are also checked.

6. Metadata Validation

KSeF verifies that the hash values and file sizes of the invoice match between the raw XML and the encrypted version. This ensures the file hasn’t been tampered with or corrupted during submission.

7. Attachments?

• Attachments are allowed, but only in batch mode.

• Exception: offline technical correction in interactive mode.

8. Permissions and Authorisation in place

• Invoices can only be submitted by individuals with proper authorisation in KSeF.

• Authorisation can be:

  • Primary – granted via the ZAW-FA form,

  • Secondary – delegated by someone holding primary rights.

Your KSeF plan to meet validation tests

At first glance, KSeF’s validation rules may look like simple technical checks. In reality, they have far-reaching consequences for how businesses structure their invoicing processes.

To comply, organisations will need to:

• Implement consistent invoice numbering systems, aligned with KSeF’s uniqueness rules.
• Pre-validate XML files against the latest XSD schema before submission.
• Adapt ERP systems to handle file size, batch limits, and metadata validation.
• Review encryption/security processes to meet KSeF’s standards.
• Set up clear user rights and authorisation procedures for KSeF submissions.