UPO from KSeF: Your Proof of Delivery and Dunning Evidence Pack

When KSeF accepts your invoice, it returns a UPO (potwierdzenie przyjęcia). The UPO is a document carrying a qualified electronic signature, a timestamp, and a hash of the submitted invoice. It is state-signed proof that your invoice was delivered to the tax system and assigned a KSeF number.

The UPO kills the "invoice never arrived" excuse. In the pre-KSeF era, buyers could claim they never received an emailed or mailed invoice. With KSeF, deemed delivery occurs when the KSeF number is assigned. The UPO is the evidence.

What the UPO Contains

• KSeF number: The 35-character invoice identifier
• Timestamp: Date and time of acceptance
• Invoice hash: Cryptographic hash of the submitted FA(3) XML
• Qualified electronic signature: State-signed, legally binding under eIDAS

The UPO is not just a receipt. It is a qualified electronic document with the same legal standing as a notarised delivery confirmation.

Archiving the UPO

Store the UPO with the invoice record. Your invoicing software should download and archive it automatically. If it does not, download it manually from Aplikacja Podatnika after each submission.

Retention period: 10 years, matching KSeF's session history retention. The UPO should be stored in a format that preserves the qualified signature (typically a signed PDF or XML file). Do not convert it to a plain PDF, which strips the signature.

Building a Dunning Evidence Pack

When a buyer does not pay, the UPO is the foundation of your evidence pack. Poland has the EU's worst late-payment problem: 53-day average delays in 2025 (Coface), with statutory interest at 14% per annum in H1 2026.

The evidence pack contains:

1. The invoice (FA(3) XML or PDF visualisation)
2. The UPO (proof of delivery to KSeF, state-signed)
3. The KSeF number (links the invoice to the tax record)
4. The wezwanie do zapłaty (formal payment demand)
5. Statutory interest calculation (14% per annum from the due date)
6. Recovery compensation (€40 for invoices under €50, €70 for €50-€5,000, €100 for over €5,000, under art. 10)

The wezwanie do zapłaty

The formal payment demand should reference:

• The invoice number and KSeF number
• The UPO date (proof of delivery)
• The original due date
• The statutory interest accrued
• The recovery compensation amount
• A new payment deadline (typically 7 days)

The UPO makes the demand credible. The buyer cannot dispute delivery. The only question is whether they will pay, not whether they received the invoice.

Deemed Receipt Under Art. 106na

Under art. 106na of the VAT Act, an invoice submitted through KSeF is deemed received by the buyer when it appears in their KSeF inbox. The buyer does not need to actively download or acknowledge it. Visibility equals delivery.

This means the buyer's VAT obligation (input VAT deduction) starts when the invoice appears in their KSeF inbox, regardless of whether they have read it. For the seller, the UPO timestamp is the delivery proof.

Statutory Interest: Automatic but Unexploited

The creditor's legal position is strong but most SMBs never charge statutory interest because the calculation and documentation are manual. A live statutory-interest meter and a one-click wezwanie do zapłaty generator turn statute into cash.

The interest rate is NBP reference rate + 10 percentage points (14% per annum in H1 2026). It accrues automatically from the day after the due date. The recovery compensation (€40/70/100) also accrues automatically per unpaid invoice.

This material is information of a general nature and does not constitute legal or tax advice. For a specific situation, verify the current rules or consult a qualified adviser.