The new definition of “delivery” and why it might be a problem

In the previous model, an invoice was issued and sent to the public contracting authority, which confirmed receipt, and from that moment on, the calculation of deadlines began.

In KSeF, this is no longer the case – the moment of delivery now has a specific, technical definition that can work to your advantage or disadvantage, depending on what is written in the contract.

The key moment is the assignment of a KSeF number to the invoice. From then on, the invoice exists in the system – legally, not just technically. If the contract states that the payment deadline runs from “delivery of the invoice,” and it is nowhere specified that this refers to the moment in KSeF, you might have a problem. The contracting authority may claim that nobody in their organization was notified that the invoice is pending in KSeF, and even if you are right, disputes and payment delays are possible.

Therefore, always gather system evidence: the KSeF number for the invoice, UPO – i.e., official confirmation of receipt of the document by the system – and ERP logs if you send the invoice automatically. Keep all of this. You will need it in the event of a dispute.

The invoice is in the system, but nobody knows about it

This may be the most frustrating aspect of KSeF from a contractor's perspective. The system does not send notifications. If the contracting authority does not have integration with KSeF or a procedure for regularly checking it, your invoice can sit there for weeks before anyone attends to it.

You can wait for it, or you can act proactively. The practice we recommend: after issuing each invoice, send a short notification to the contracting authority – by email or via the platform – containing the invoice number, KSeF number, and the date this number was assigned. Optionally, attach the UPO. This does not replace KSeF or change the moment of delivery, but it significantly reduces the risk of a situation where “nobody saw anything in the office, so they didn't pay.”

There is no edit option – you handle the correction

In many public organizations, a simple mechanism has existed until now: an invoice with an error is returned to the contractor with a note “to be corrected,” the contractor corrected it in the system and sent the correct version. In KSeF, this is physically impossible.

An invoice that has entered the system stays there. If it is incorrect, the only path to remedy the situation is a corrective invoice, which is the contractor's responsibility. And the contracting authority may hold payment precisely because something is wrong – even if it is a minor mistake in the item description or the contract number.

The practical conclusion is simple, but requires discipline: the quality of data on the invoice must be flawless. Compliance with the contract and SWZ (Terms of Reference) is not a matter of formality – it is a matter of how quickly you get paid.

PEF still exists. How to use it?

In public procurement, PEF – the electronic invoicing platform – is not going away. With good integration, an invoice sent to PEF can be automatically forwarded to KSeF, without manual copying.

For the contractor, this can be an operational advantage. If the contracting authority “lives” in PEF and has processes implemented there, PEF can be your working channel, and KSeF – the formal confirmation of delivery of the document. But one thing is crucial: the contract must clearly state which moment is considered the “receipt” of the invoice – KSeF or PEF. Without this, you do not know when the payment deadline starts counting.

What to look out for in the SWZ and the contract before you sign it

Three things worth paying attention to:

• Invoicing channel
  Does the contract mention KSeF at all? Does it permit PEF? What happens in cases legally excluded from KSeF – failures, statutory exceptions? If this is missing, ask the contracting authority.

• Moment of receipt of the invoice and the start of the payment deadline
  This is the most important provision. If the contract says that the payment deadline starts from the assignment of the KSeF number – you are secure. If it says nothing, or says “from entry into circulation” or “from approval” – the risk increases. Try to get this clarified.

• Communication and evidence
  If the contract requires you to provide additional notification – make sure this is an “auxiliary” requirement, and not a condition upon which the moment of invoice receipt depends. This is a subtle but important distinction.

Contracts already signed: when it is worth pushing for an amendment

If you have ongoing contracts where the delivery mechanism is based on paper, email, or document workflow portals – the risk increases. The larger the amounts, the more invoices, and the tighter the cash flow, the more it is worth trying to sign an amendment.

The good news: changing invoicing provisions in ongoing contracts is usually treated as a non-material change in accordance with Art. 454 of the Public Procurement Law (PZP).

Transition period: peace of mind for the contracting authority, risk for the contractor

The Ministry of Finance is signaling a soft approach in 2026 – no penalties for errors and delays in implementation. For the contracting authority, this means a little more time to adapt. For you as a contractor, it means something else.

Your risk does not lie in penalties. It lies in the fact that the contracting authority may not be ready to receive invoices and pay on time. The transition period does not protect your cash flow – it only protects the contracting authority from sanctions. That is why your process readiness – quality of invoices, system evidence, communication – matters from day one.

What to do now: checklist for the contractor

1. Organize the data on invoices – contract number, buyer details, item description. Zero surprises.

2. Automate evidence – KSeF number, UPO, ERP dispatch logs. Keep them in one place.

3. Implement a notification habit – after each invoice, a short email to the contracting authority with the KSeF number.

4. Review contract templates and SWZ – verify clauses on “invoice delivery” and the “start of payment term.”

5. Prepare an amendment template for ongoing contracts and propose the change – do not wait for the contracting authority to take the initiative.

6. Train your team on the changes – so they know how to spot risky provisions before you sign them.

*__KSeF changes the rules of the game for both sides. But for the contractor, the stakes are higher: payment terms, cash flow, and the certainty that the invoice will be processed. The faster you implement the new processes, the fewer surprises there will be