National e-Invoice System (KSeF) is the central system of the Ministry of Finance for issuing and sending invoices in a standardized XML format. From February 1, 2026, every entrepreneur in Poland is required to issue invoices through this system. For accounting offices, this means a change not only technically but also in the entire workflow of handling clients' documents.

In this article, you will find:

• What changes KSeF brings to the daily work of an accounting office

• Which processes you need to adapt and how to do it

• How AI can reduce the handling time of KSeF documents by 60-70%

• A complete checklist for preparing the accounting office

What is KSeF and what does it change for accounting offices?

KSeF (National e-Invoice System) replaces the decentralized sending of invoices with a unified central system. Client invoices are no longer PDF files or paper documents - they are now structured XML data with the KSeF number as a unique identifier.

For accounting offices, this primarily means:

• New obligations related to integrating accounting systems with the KSeF API

• Change in the flow of documents from clients to the office

• The need to handle client inquiries regarding errors and rejections in KSeF

• An opportunity for complete automation of document processing

Good news: invoices in XML format are significantly easier to process automatically than images or scans. This opens doors to automation that was previously impossible to achieve.

What challenges does KSeF create for accounting offices?

According to data collected by industry experts, accounting offices identify 4 main challenges in implementing KSeF:

1. System integration

Most offices use accounting software (Comarch, Symfonia, Sage), which must be integrated with the KSeF API. Without this integration, work becomes manual and many times more time-consuming.

2. Changing client habits

Clients of accounting offices must issue invoices through KSeF - not everyone understands this or does it correctly. Offices must support clients in the onboarding process.

3. Handling errors and rejections

KSeF rejects invoices with formal errors (incorrect NIP, missing fields, incorrect VAT rates). Each rejection requires contacting the client and making corrections - extra time for the office.

4. Document volume

Offices that previously accepted invoices in PDF or paper must now handle the same volume in a new format - without a proportional increase in employment.

How is AI changing the handling of KSeF documents?

Traditional workflow: the client sends an invoice → the office worker manually re-enters data → data goes to the accounting system.

Time: 3-5 minutes per invoice.

AI-powered workflow: XML invoice from KSeF → AI automatically validates, maps, and posts → data goes to the system.

Time: 8-15 seconds per invoice.

Accounting offices using AI to process KSeF documents can handle twice as many clients without a proportional increase in employment.

Specific tasks that AI automatically performs:

1. NIP data validation - checking the correctness of the NIP number of the contractor in the GUS register

2. Mapping to accounting accounts - assigning the invoice to the appropriate cost category based on history

3. Duplicate detection - identifying invoices that may have been submitted twice

4. Flagging anomalies - flagging invoices with values deviating from the norm

5. Generating postings - preparing proposal for postings based on previous patterns

Practical checklist: how to prepare the accounting office for KSeF

Step 1 - Technical

• Check if your accounting software has integration with the KSeF API

• Create an account in the KSeF system for the office (ksef.gov.pl)

• Register as an entity authorized to act on behalf of clients

• Test issuing a test invoice through KSeF

• Set up notifications for invoice rejections

Step 2 - Operational

• Develop a new client onboarding checklist (with KSeF as a mandatory step)

• Prepare a guide for clients on how to issue invoices through KSeF

• Create a template response for the most common rejection errors

• Establish a workflow: what happens when a client's invoice is rejected by KSeF?

• Determine who in the office is responsible for monitoring rejections

Step 3 - Automation

• Evaluate whether your current tool supports automatic downloading of invoices from KSeF

• Check AI solutions for automatic postings (e.g., Clereo, SaldeoSMART AI)

• Calculate how much time you lose monthly due to manual data entry

• Identify clients with the highest number of invoices - they will benefit the most from automation

• Test automation on one client before implementing it throughout the office

Frequently asked questions about KSeF 2026

Do invoices from foreign clients also have to be in KSeF?

No. KSeF applies to B2B transactions between Polish entrepreneurs. Invoices for foreign entities, consumer invoices (B2C) and certain special transactions are excluded from the KSeF obligation.

What if the KSeF system does not work?

The Ministry of Finance provides for an emergency mode - invoices can be issued offline and sent to KSeF when the system is back up. The office must have a procedure for such situations.

Does KSeF change the invoice retention periods?

Invoices in KSeF are stored by the Ministry of Finance for 10 years. The office still has to keep its own copies and related documents, but the risk of losing an invoice practically disappears.

How does KSeF affect the prices of accounting office services?

Many accounting offices have updated their price lists to account for the additional time for handling KSeF and training clients. Offices with AI automation can maintain competitive prices despite higher technical requirements.

Summary

KSeF is a change, but also an opportunity. Accounting offices that implement AI automation for processing KSeF documents can serve more clients at the same time - without a proportional increase in costs.

Three steps to take this week:

1. Check the status of your software's integration with KSeF

2. Count how many invoices your office processes monthly

3. Calculate how many hours you would save monthly with automatic processing

If you want to see how AI processes KSeF invoices in practice - visit Clereo.co or write to us directly.