IPKSEF_FORMAT: IPKSeF must be exactly 13 alphanumeric characters…

StandardKSeF FA(3), Polish national e-invoicing systemSeverityWarning: the invoice is accepted but should be correctedSyntaxFA(3) XMLApplies toStructured invoices (FA(3) schema) submitted to the Polish KSeF. XSD codes come from the schema, semantic codes from the Ministry of Finance information sheet; KSeF rejects invoices that fail an error-level rule.

Official rule text

[IPKSEF_FORMAT] IPKSeF must be exactly 13 alphanumeric characters [0-9a-zA-Z] (§12.1)

Why this error occurs

KSeF checks the FA(3) XML in two stages: XSD schema (structure, element order, data types, patterns such as NIP or dates) and semantic rules from the Ministry of Finance information sheet (consistency of amounts, annotations P_16 to P_23, roles of Podmiot2/Podmiot3, bank account formats, currency rates).

How to fix it

Fix the element named in the message. For XSD errors compare the element order and value pattern with the FA(3) schema; for semantic errors apply the cause and fix hints listed on this page. Re-validate before submitting to KSeF: a rejected invoice has no KSeF number and is not issued.

What the validator checks

Check levelsemantic / format

Typical causes

Invalid IPKSeF format
Wrong length
Non-alphanumeric characters

Check your invoice

Drop your XML or PDF on the validator and every failed rule is linked to its page here. Free, no account, the file is not stored.

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Same check via API:

curl -F file=@invoice.xml https://einvoicechecker.com/v1/validate

Related rules

AMOUNT_NO_SEPARATORS Amount fields must not contain spaces, commas, or any non-numeric characters except…
DECIMAL_PRECISION Amount field exceeds maximum decimal precision defined in §2.6 of FA(3) specification
GTU_FORMAT GTU value must match pattern GTU_XX (GTU_01 through GTU_13)
INVALID_BANK_ACCOUNT_FORMAT Polish bank account (NrRB) must be 28 characters for IBAN format (PL + 26 digits) or…
NRRB_LENGTH NrRB must be 10–34 characters (§12.1)

Frequently asked questions

What does IPKSEF_FORMAT mean?

IPKSEF_FORMAT is a ksef fa(3) rule: IPKSeF must be exactly 13 alphanumeric characters [0-9a-zA-Z] (§12.1)

Will my invoice be rejected because of IPKSEF_FORMAT?

No. IPKSEF_FORMAT is a warning: the invoice is accepted but the recipient sees the notice. Fix it anyway, warnings often become errors in later rule versions.

Which formats does IPKSEF_FORMAT apply to?

Structured invoices (FA(3) schema) submitted to the Polish KSeF. XSD codes come from the schema, semantic codes from the Ministry of Finance information sheet; KSeF rejects invoices that fail an error-level rule. Syntax: FA3.

Source: KSeF FA(3) schema 1-0E + semantic rules (@ksefuj/validator 0.4). Catalogue generated from the official rule sets on 2026-10-15.

IPKSEF_FORMAT: IPKSeF must be exactly 13 alphanumeric characters [0-9a-zA-Z] (§12.1)