KSEF-21181
Error Guide
🇵🇱 KSEF-21181: Sellers are not identical for all invoices in a KSeF batch in Poland
ErrorMandatoryManual Fix
The KSeF 2.0 API rejected a batch session because at least one invoice inside the batch has a Podmiot1 (issuer) NIP that differs from the others. KSeF requires every invoice in a single batch session to belong to the same seller.
Quick Facts
Severity
Error (rejection)
Ruleset
KSeF 2.0
Fix Confidence
0%
Mandate
B2B Mandatory
Fix Type
Manual
Why This Matters in Poland
Poland requires e-invoicing using KSeF XML format. Invoices with this error will be rejected. They cannot be processed for Poland compliance.
Invoice Navigator covers 134 KSeF FA(3) rules for Poland.
How to Fix KSEF-21181
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Poland E-Invoicing Requirements
Phase
Status
Scope
KSeF voluntary
Live (Jan 2022)
All VAT payers (opt-in)
B2B mandatory — Phase 1
Live (Feb 1, 2026)
Large taxpayers (>200M PLN turnover)
B2B mandatory — Phase 2
Live (Apr 1, 2026)
All remaining VAT-registered entities (SMEs, sole proprietors, VAT-exempt businesses)
B2G
Live (Feb 1, 2026)
Included in general KSeF mandate
Financial penalties
Jan 1, 2027
Up to 100% of VAT amount on non-compliant invoices
Common Causes
- •Accounting firm submits invoices from multiple client NIPs in one export job
- •Shared service centre batches subsidiaries together
- •ERP export incorrectly uses buyer NIP instead of seller NIP as the grouping key
- •Test data mixed with production data in a single batch
Fix KSEF-21181 automatically
Upload your invoice and let Invoice Navigator auto-remediate this error.