Advance Invoices in KSeF for Small Businesses

An advance invoice in KSeF is a structured FA(3) invoice that documents receiving all or part of the payment before the supply or service is performed, if the specific transaction requires such a document. In the FA(3) structure, it corresponds to the ZAL type.

For a small business, the biggest risk is not issuing the advance invoice itself. The real risk appears later, when the order, advance invoice, KSeF number, UPO, payment, settlement invoice and possible correction all have to be connected.

If earlier advance invoices do not cover the full payment, after the transaction is completed you need a settlement or final invoice, usually type ROZ, reduced by the advances already settled. If the advance covers 100% of the value, do not automatically assume that an additional final invoice is needed - check the specific case with accounting.

A small service business often takes an advance before doing the work: for a website project, training, catering, renovation, booking a date or custom production. After mandatory KSeF comes into force, it is not enough to record the payment in a spreadsheet and return to it at final settlement.

If the advance requires an invoice, the document is a structured invoice. That means FA(3) XML, the correct document type, buyer data, the amount received, VAT, timing, the seller's own invoice number and later the KSeF number after the system accepts it.

This article reflects the state as of June 24, 2026 and is a practical guide for businesses that have already organized the basics in KSeF for small businesses and now need to handle advances, final invoices and corrections.

1. When an advance invoice is issued

2. Deadline for issuing an advance invoice

3. Document types ZAL, ROZ, KOR_ZAL and KOR_ROZ

4. Final invoice after an advance

5. How to store the KSeF number and UPO for an advance

6. Process for a small business

7. Common mistakes with advances

8. How KSeFGPT helps with advances

An advance invoice appears when a business receives payment before performing the transaction and the regulations require that payment to be documented with an invoice. For a small business, typical cases include booking a date, a project stage, prepayment for goods, an advance for a service or the first installment of a larger order.

Not every payment commonly called an advance has the same tax treatment. A deposit, earnest money, payment for a continuous service or payment covered by special rules may be treated differently. This article shows the operating process, but the tax decision for unusual cases should be confirmed with accounting.

In KSeF, the key point is that an advance invoice is not a loose payment note. After submission and acceptance, it receives a KSeF number and UPO and becomes part of a document chain that later has to be linked to a settlement invoice or correction.

The VAT Act sets the general rule that an invoice documenting receipt of all or part of the payment before the transaction should be issued no later than the 15th day of the month following the month in which the payment was received. This is the final deadline, not an invitation to postpone the document.

In practice, KSeF rewards quick organization. If the payment arrived on June 10, the business should issue the ZAL as soon as reasonably possible, submit the FA(3) XML, download the UPO and store the KSeF number. Waiting until the middle of the next month increases the risk of mixing up orders and amounts.

An invoice issued before payment requires caution, because the rules limit invoicing too early. A safe procedure for a small business is simple: first confirm the receipt of funds or the payment terms with accounting, then issue the invoice with the correct type, and only then close the stage in the system.

In FA(3), the document type matters. An ordinary sales invoice, corrective invoice, advance invoice and settlement invoice are not the same operational case. The local KSeFGPT validator recognizes, among others, VAT, KOR, ZAL, ROZ, KOR_ZAL and KOR_ROZ.

For advances, the two most important steps are these: ZAL documents the payment received before the transaction is performed, and ROZ organizes the final settlement after earlier advances. If the advance or settlement invoice has to be corrected, KOR_ZAL or KOR_ROZ comes into play.

This distinction helps avoid confusion. If a business issues an ordinary VAT document instead of ZAL, accounting may lose the information that the document related to a payment before the service was performed. If the business fails to link ROZ to earlier advances at final settlement, the amounts may look like duplicated sales.

A final invoice after an advance is needed when earlier advance invoices do not cover the full payment for the supply or service. In that case, the final document should settle the full transaction value but reduce it by the amounts and VAT already shown on the advance invoices.

In KSeF, this practically means a ROZ settlement invoice with references to earlier ZAL invoices. It is worth storing the seller's own advance invoice numbers, dates, amounts, KSeF numbers and UPOs. Without this, the final document may be mathematically correct but hard to defend from a process perspective.

If the advance covered the whole payment, do not automatically create an additional final invoice only because the project has ended. This case should be checked with accounting, because an extra document may duplicate the settlement instead of organizing it.

After submitting an advance invoice, the two most important confirmations are the KSeF number and UPO. The KSeF number identifies the document in the system, and UPO confirms acceptance. The invoice number from field P_2 alone is not enough, because it is assigned by the business, not by KSeF.

For advances, you need to store more data than for a simple invoice. You need the order or contract number, the date the money was received, the advance amount, information on whether it is a partial or full payment, the advance invoice number, KSeF number, UPO and settlement status.

If you later issue ROZ, this data must come back. A good practice is to treat advance invoices as a set of linked documents, not as separate individual files. The identifier itself is explained in more detail in KSeF number on an invoice.

The simplest process starts before the payment. Agree with the customer whether the payment is an advance, which order it relates to, the gross amount, the applicable VAT rate and when the service or delivery will be performed. This data should enter the system before the money arrives in the account.

After the funds arrive, issue ZAL, validate the FA(3) XML, submit the invoice to KSeF and download the UPO. Then mark the advance as waiting for settlement. After the service is performed, check whether ROZ is needed or whether the earlier advances covered the whole payment.

If the order scope, number of participants, date, price or the customer's decision changes along the way, do not manually rewrite the history in a spreadsheet. Check whether you need a ZAL correction, ROZ correction or a new settlement. If in doubt, return to the guide Corrective invoice in KSeF.

Mistakes with advances usually do not look serious on the day the document is issued. The problem appears later, when the business has to issue a settlement invoice, prepare JPK, explain a payment or correct an order.

The most common mistake is no link to the order. The second is missing KSeF number and UPO in the internal register. The third is issuing an ordinary VAT invoice instead of ZAL, or issuing the final document without deducting earlier advances.

In KSeF, every stage leaves a trace, so confusion cannot be fixed by renaming a PDF file. You need correct XML, the right document type, KSeF numbers and consistent amounts. If the document is rejected, start with the diagnostics described in Invoice rejected by KSeF.

KSeFGPT does not replace accounting and does not make the tax decision for the business. It helps organize the data that is easiest to lose with advances: contractor, order, document type, line items, amounts, KSeF number, UPO and later settlement.

For a small business, continuity is the key. In one process, you can prepare the invoice, check the XML, submit the document, monitor statuses and return to the invoice for settlement or correction. As a result, the advance invoice does not remain an isolated PDF in an email.

If you work with many customers, advances and corrections, use KSeFGPT as an application for KSeF invoices, import, export, validation and data organization for accounting. It is a natural extension of the process described in KSeF for small businesses.