PL-R-004:KSeF session token invalid
KSeF API requires valid authentication token.
Engine Classification
Financial or legal field · Modification blocked by policy
Reason: KSeF API authentication token is invalid or expired. This is not an invoice content issue. Renew your KSeF session token through the KSeF API authentication process. Check your invoicing software KSeF credentials configuration.
What is PL-R-004?
PL-R-004 is a fatal validation rule defined in the ubl-2.1 specification (POL national rules). It validates the KSeF API authentication element in the UBL invoice XML.
When this rule fires, the invoice is non-compliant and will be rejected by Peppol access points and national validation services. The sending system receives a rejection response and the invoice does not reach the buyer.
Target path: KSeF API authentication
Why This Error Matters
Authentication required for KSeF operations.
PL-R-004 is a hard failure. Invoices that trigger this rule are rejected at the access point and never reach the recipient. In Peppol networks, this means your sending system receives an MLR (Message Level Response) with a rejection status. The invoice must be corrected and re-sent, adding delay to your payment cycle.
Validator Behavior
- ·Causes invoice rejection
- ·Fails UBL schema validation
- ·Error returned: PL-R-004
- ·Specification: ubl-2.1
How to Fix It
Authenticate
Use qualified certificate or trusted profile
Get token
Call InitSessionBySignature
Use token
Include in subsequent API calls
XML Example
Generic example based on the rule's target XPath. Your actual XML structure may differ.
<!-- Triggers validation error --> <KSeF API authentication></KSeF API authentication>
<!-- Corrected --> <KSeF API authentication>VALID_VALUE</KSeF API authentication>
Technical Reference
KSeF API authenticationCommon Causes
- ·Expired token
- ·Invalid certificate
- ·Wrong authentication method
Seeing this in production? The API handles PL-R-004 automatically. See the fix response →
Frequently Asked Questions
KSeF API requires valid authentication token.
Obtain valid KSeF session token using certificate or trusted profile. This error involves a protected field — Invoice Navigator flags it in your pipeline so your team can correct it at the source.
Yes, PL-R-004 is a critical error that will cause invoice rejection. It must be fixed before submission.
Related Content
Last updated: 3 March 2026
Detect PL-R-004 Before Submission
This error involves a financial or legal field that cannot be auto-modified. The compliance engine flags it immediately with a clear diagnosis so your team can fix it at the source.