Corrective Invoice - KOR - KSeF

What is supported in KSeF for corrections

What is supported in KSeF:

• A "Credit Note" does not exist as a specific document type in KSeF
• The supported document type is KOR, it allows:
  • Supported :
    • Corrections to compare with a credit note, where you credit some/all lines compared to the invoice, can be a credit of the complete invoice or a part. Per line you can specify the quantity (full quantity or a part) and the price (same unit price or a different unit price)
    • Each line contains the net info about the line.
  • Currently not supported :
    • other types of corrections e.g. : change in customer and supplier data.
    • Indicate per line the info before correction and after correction

Sending a Corrective Invoice via Billit

Billit currently supports the above scenario 1.

How it works:

• Via Billit you can create a credit note,
• it will automatically be converted to KOR. This can be created via the normal Billit ways:
  • Via API.
  • Manual creation via MyBillit user interface.
  • UBL upload.
• Reference to the Invoice:
  • The reference to the linked invoice must be included in case of KSeF (API : AboutInvoiceNumber).
  • You can only refer once to an invoice number when sending credit notes, and the total amount of the credit note should not exceed to amount of the invoice.
• How to create a credit note via API : see general credit note info page : https://docs.billit.be/docs/sending-a-credit-note
• The credit note will appear in the menu Income / Credit Notes.

Specific fields:

Not supported:

• Separate Correction Note (nota korygująca, optional)

Positive Amounts to Billit, negative amounts in KOR

To Billit, info is sent as a normal credit note:

• Json content has positive amounts. General info see https://docs.billit.be/docs/sending-a-credit-note
• In Billit, it contains positive amounts (including on PDF generated by Billit).

Billit KSeF XML:

• In the KSeF XML of the KOR, the amounts are set to negative by Billit.

Below a KSeF XML example, with just 3 detail lines. The amounts are negative.

   <FaWiersz>
      <NrWierszaFa>1</NrWierszaFa>
      <P_7>Test Article 1</P_7>
      <P_8A>MTR</P_8A>
      <P_8B>6.50000</P_8B>
      <P_9A>-34.96000</P_9A>
      <P_11>-227.24</P_11>
      <P_12>23</P_12>
    </FaWiersz>
    <FaWiersz>
      <NrWierszaFa>2</NrWierszaFa>
      <P_7>Test Article 2</P_7>
      <P_8A>MTR</P_8A>
      <P_8B>110.50000</P_8B>
      <P_9A>-21.41004</P_9A>
      <P_11>-2365.81</P_11>
      <P_12>23</P_12>
    </FaWiersz>
    <FaWiersz>
      <NrWierszaFa>3</NrWierszaFa>
      <P_7>Test Article 3</P_7>
      <P_8A>MTR</P_8A>
      <P_8B>13.00000</P_8B>
      <P_9A>-27.80000</P_9A>
      <P_11>-361.40</P_11>
      <P_12>23</P_12>
</FaWiersz>    

Specific Corrective Invoice Fields in the KSeF XML

Below an KSeF XML example with comments (the main KOR-section of the file).

<Fa>
    <RodzajFaktury>KOR</RodzajFaktury>  //doctype is KOR
  <TypKorekty>2</TypKorekty> //Type of correction. 2 : correction with effect on the date of issue of the
corrective invoice,
    <DaneFaKorygowanej>
      <DataWystFaKorygowanej>2026-02-20</DataWystFaKorygowanej>  //Corrected Invoice Issue Date]
      <NrFaKorygowanej>00008</NrFaKorygowanej>  //Number of the correction of the previous document (example previous KOR document)
      <NrKSeF>1</NrKSeF>  //Flag of the KSeF number of the corrected (original)
invoice
      <NrKSeFFaKorygowanej>9540010231-20260220-371693400000-9B</NrKSeFFaKorygowanej>  //Corrected Invoice KSeF
Number, so this is referring to the original document, but then the KSeF number
		</DaneFaKorygowanej>  
</Fa>

During the Transition Period

When starting with KSeF, you might need to to issue a corrective invoice where the invoice number you refer was delivered via email before starting with KSeF.

Options:

• Scenario 1: Invoice via Billit
  • First upload the original invoice in Billit and send it to KSef via Billit.
  • Then send the corrective invoice with reference to the original invoice.
• Scenario 2 : No invoice via Billit, submit corrective invoice using extra fields, variants:
  • Scenario 2a - You do not have a KSeF Reference of the Original Invoice
  • Scenario 2b - You have a KSeF Reference of the Original Iinvoice

Status of scenario 2:

• available on sandbox
• not yet operational (will be updated soon)

More info about the Extra fields (header level):

Scenario 2a - You do not have a KSeF Reference of the Original Invoice

	"CustomFields": {
        "Faktura.Fa.DaneFaKorygowanej.DataWystFaKorygowanej":"2026-03-31", //InvoiceDate of the original invoice.
        "Faktura.Fa.DaneFaKorygowanej.NrFaKorygowanej":"2026-00178",// InvoiceNumber of the original invoice.
        "Faktura.Fa.DaneFaKorygowanej.NrKSeFN": "1" // The original invoice is not in KSeF
    }

Scenario 2b - You have a KSeF Reference of the Original Iinvoice

"CustomFields": {
        "Faktura.Fa.DaneFaKorygowanej.DataWystFaKorygowanej":"2026-01-31", //InvoiceDate of the original invoice.
        "Faktura.Fa.DaneFaKorygowanej.NrFaKorygowanej":"2026-00122",// InvoiceNumber of the original invoice.
        "Faktura.Fa.DaneFaKorygowanej.NrKSeFFaKorygowanej":"5471766193-20260331-600142000000-40" //KSeFReference Number
        "Faktura.Fa.DaneFaKorygowanej.NrKSeF": "1" // Original invoice is in KSeF
    }

Receiving a Corrective Invoice in Billit

When a corrective invoice is received from supplier, below the current way of working. This will evolve in the near future.

Receiving corrective invoice:

• The corrective invoices arrives in the Fast Input. It includes the human readable.
• After manual processing KOR can be viewed in menu Expenditure / Credit Notes.
• Details screen contains the KSeF information (PDF not yet).
• KSeF info can also be viewed on the Polish KSeF portal.