KSeF and an accounting firm: what should the agreement cover after mandatory e-invoicing?

KSeF changes how businesses work with their accountants

From 1 February 2026, the obligation to issue invoices through KSeF applied to the largest taxpayers, and from 1 April 2026 it covered most other businesses. As a rule, receiving invoices through the system has been mandatory since 1 February 2026.

A transitional simplification remains available to the smallest businesses until the end of 2026. A taxpayer whose total monthly sales documented by invoices issued outside KSeF do not exceed PLN 10,000 gross may continue to use the existing invoicing method. Once the threshold is exceeded, however, the obligation applies from the invoice that causes the threshold to be exceeded.

Even a business using this simplification should agree with its accounting firm how purchase invoices will be retrieved and prepare for a full transition to the system.

A KSeF permission is not a contractual obligation

A business may grant an accounting firm or designated individuals permission to issue invoices, access invoices or manage further permissions.

Granting access does not mean that the accounting firm has accepted an obligation to perform specific tasks. Holding a KSeF permission does not, by itself, create an obligation to act.

The agreement must therefore allocate the activities to be performed by each party. Without these arrangements, each side may assume that a particular task belonged to the other.

• whether the firm only retrieves and books invoices or also issues them;
• who approves the data before an invoice is submitted;
• who monitors incoming purchase invoices;
• who prepares corrections;
• who responds if a document is rejected or no KSeF number is assigned;
• who handles contingency procedures.

Who is responsible for the invoice content?

An accounting firm may prepare an invoice using information provided by the client, but it will not always be able to determine independently whether a service has been performed, when the tax point arose or whether an agreed price includes a discount.

The agreement should divide responsibility for commercial and tax data. The business may be responsible for supplying information about the transaction, customer, amount and performance date. The accounting firm may be responsible for entering the information correctly, applying the agreed accounting treatment and submitting the invoice technically.

Advance payments, corrective invoices, self-billing, cross-border transactions and split-payment transactions may require dedicated procedures. The parties should also identify situations that the accounting firm must refer for additional advice instead of relying on an unverified assumption.

Approving an invoice before submission

In the simplest model, the business provides complete data and the accounting firm issues the invoice without further approval. For more complex transactions, it may be safer for a designated person on the client side to approve a draft.

The process can also be divided by category. Standard subscription invoices may be issued automatically, while documents above a specified value, involving a foreign customer or using an unusual VAT rate may require approval.

The agreement or an operational appendix should state how much time the client has to approve the invoice and what happens if no response is received. The accounting firm should not have to choose between missing the deadline and issuing an unapproved document.

Receiving purchase invoices requires a new process

An invoice may arrive in KSeF without first being emailed to the person who ordered the service. Its retrieval by the accounting firm does not confirm that the performance took place or that the business accepted it.

The business should establish an internal cost-approval workflow. The accounting firm should not be responsible for the substantive approval of an expense if it was not involved in the transaction.

• whether the responsible person recognises the supplier;
• whether the order has been performed;
• whether the amount matches the agreed terms;
• which project or cost centre should receive the expense;
• whether there are grounds to dispute the invoice.

Offline mode, outages and delayed submission

KSeF provides special procedures for system unavailability and problems on the taxpayer's side. Using the appropriate mode may require specific invoice markings, a certificate and submission to the system within a prescribed period.

The agreement should identify who decides to use an offline mode and who monitors the subsequent submission. It should also distinguish an outage of the government system from a failure of the accounting software or the client's infrastructure.

If the accounting firm has not been informed that the business's sales system is unavailable, it should not automatically be responsible for a document it never received.

Security of permissions and access

A shared account or the transfer of login credentials makes it difficult to determine who performed a specific action. A safer model uses individual permissions assigned according to each person's responsibilities.

The business should periodically review who can access its invoices. The agreement may require the accounting firm to report changes to the staff handling the account, the use of subcontractors and access-related incidents.

The parties should also decide who revokes permissions when the relationship ends. A person with access cannot remove their own permission; it must be withdrawn by a person authorised to manage access in the taxpayer's context.

What should a KSeF amendment include?

The parties do not always need to replace the entire accounting services agreement. An amendment accompanied by an appendix describing the document workflow will often be sufficient.

The procedure should reflect how the business actually works. Copying a generic clause referring to 'KSeF support' will not resolve operational issues.

• the scope of activities performed in KSeF;
• the allocation of responsibility for data;
• methods and deadlines for supplying information;
• the invoice approval procedure;
• corrections and contingency procedures;
• granting and revoking permissions;
• the response to identified errors;
• liability for delays;
• the transfer of data when the engagement ends.