If you operate a property in Poland and issue invoices in Mews Operations, you need to submit eligible business invoices through the national KSeF platform to meet legal requirements. You perform this action when you issue invoices for business-to-business or business-to-government transactions. This applies from February 2026 for large entities and from April 2026 for all other VAT-registered businesses in Poland. When the KSeF Fiscal Registry Integration is active, Mews automatically submits eligible invoices to KSeF for validation and legal issuance.

 

In this article, you can learn about:

• How to send compliant B2B and B2G invoices to KSeF in Mews Operations
  • What you need before sending invoices to KSeF
  • How KSeF invoicing works in Mews
  • How to send an invoice to KSeF
  • How to check invoice status after submission

 

How to send compliant B2B and B2G invoices to KSeF in Mews Operations

What you need before sending invoices to KSeF

Before you send invoices, ensure you complete the following setup:

• The KSeF Fiscal Registry Integration is active for your property
• Your company details are complete, including registered name, address, and NIP
• You upload your KSeF certificate, private key, and password
• Your customer profiles include a valid NIP for each business you invoice

How KSeF invoicing works in Mews

KSeF is a centralized government system that validates and registers invoices before they are legally issued. This process follows a clearance model.

 

In Mews Operations, when the integration is active:

• Mews sends eligible invoices to KSeF automatically in the background
• The invoice is converted into the required structured format
• KSeF validates the invoice and assigns a unique KSeF identification number
• The invoice becomes legally issued only after validation

 

Note: This process applies only to business-to-business and business-to-government invoices for VAT-registered entities in Poland. It does not apply to invoices for private customers.

 

How to send an invoice to KSeF

Follow these steps to issue and submit an invoice:

1. Open Mews Operations.
2. Navigate to the Billing or Invoices section.
3. Select the invoice you want to issue.
4. Confirm that the invoice includes complete company details and a valid NIP for the buyer.
5. Finalize the invoice.

If the integration is active and the invoice meets KSeF requirements, Mews automatically submits the invoice to KSeF for validation.

 

How to check invoice status after submission

After submission, you can track the invoice status in the Fiscal record Report in Mews Operations.

• Pending validation
  • The invoice is sent to KSeF and awaits validation
• Success
  • KSeF validates the invoice
  • A unique KSeF identification number is assigned
  • A QR code appears on the invoice for verification
• Error
  • KSeF does not validate the invoice
  • You need to correct the data and finalize the invoice again

 

For example, if the buyer NIP is incorrect, the invoice is rejected and you need to update the company profile before resubmitting.