Reverse charge: P_18 doesn't match the VAT rate

What this message means

Two parts of the invoice disagree about reverse charge, that is, about whether the buyer accounts for the VAT. Either the summary contains sales outside Poland or under domestic reverse charge while the "reverse charge" flag is off, or the flag is on and no line has a matching rate. The FA(3) schema doesn't link these fields, which is why this is a warning rather than a blocking error.

The validator raises it in two situations:

• Fa contains P_13_8 (supplies outside Poland) or P_13_10 (domestic reverse charge), but Adnotacje/P_18 isn't 1;
• P_18 is 1, but no invoice line has the rate np I, np II or oo (in FaWiersz the field is P_12; on an advance invoice, ZamowienieWiersz uses P_12Z).

Why these fields must agree

P_18 is the "reverse charge" (odwrotne obciążenie) annotation. According to its description in the schema, you enter 1 when the buyer is obliged to account for value added tax or a similar tax, and 2 otherwise (MF FA(3) information brochure, or broszura, description of P_18 in Adnotacje). The rates in the lines describe the same thing from the other side (description of P_12): oo is domestic reverse charge, np I is a supply outside Poland, and np II covers services under Art. 100 ust. 1 pkt 4 of the VAT Act. The amounts from these lines go into P_13_8, P_13_9 and P_13_10.

The description of P_13_8, however, doesn't depend on who accounts for the tax: the field covers supplies outside Poland other than the amounts in P_13_5 and P_13_9, and the brochure gives services taxed where determined under Art. 28e of the VAT Act as an example. If you, not the buyer, account for the tax on such a sale, P_18 = 2 is consistent with the field description and you can ignore the warning. That won't be the case with P_13_10, because there the buyer is the taxpayer. If you're not sure which case applies to your invoice, ask your accountant.

How to fix it

1. Establish whether the buyer accounts for the VAT on this sale.
2. If they do, set P_18 to 1 and check that the lines have the rate np I, np II or oo.
3. If they don't, set P_18 to 2 and keep the rate that actually applies in the lines (for example 23 or 0 WDT).

Example: a service for a business outside the EU that accounts for the tax in its own country.

<!-- ❌ Amount in P_13_8, but P_18 = 2 -->
<Fa>
  <KodWaluty>PLN</KodWaluty>
  <P_1>2026-10-08</P_1>
  <P_2>FV/10/2026</P_2>
  <P_13_8>4000.00</P_13_8>
  <P_15>4000.00</P_15>
  <Adnotacje>
    <P_16>2</P_16>
    <P_17>2</P_17>
    <P_18>2</P_18>
    ...
  </Adnotacje>
  <RodzajFaktury>VAT</RodzajFaktury>
  <FaWiersz>
    <NrWierszaFa>1</NrWierszaFa>
    <P_7>Projekt identyfikacji wizualnej</P_7>
    <P_11>4000.00</P_11>
    <P_12>np I</P_12>
  </FaWiersz>
</Fa>
<!-- ✅ P_18 = 1, consistent with the np I rate in the line -->
<Adnotacje>
  <P_16>2</P_16>
  <P_17>2</P_17>
  <P_18>1</P_18>
  ...
</Adnotacje>

The reverse situation is P_18 = 1 on lines with an ordinary rate, such as 23. If you're charging the tax yourself, set P_18 to 2. If the buyer really does account for the VAT, correct the rates in the lines.

Next step

The fields for a foreign buyer and how to choose between np I, np II, 0 WDT and 0 EX are covered in our post on invoicing a foreign buyer, and the full Adnotacje block in the most common FA(3) validation errors. Once you've fixed it, check the invoice again.