XML-004:Invalid XML characters
Fix: Remove or encode invalid characters.
Document contains invalid XML characters.
Engine Classification
Financial or legal field · Modification blocked by policy
Reason: The document contains characters that are invalid in XML (control characters, incorrectly encoded bytes, etc.). This is typically caused by encoding mismatches or copy-paste from non-standard sources. Fix the source data in your ERP/invoicing system to use valid UTF-8 characters.
What is XML-004?
XML-004 is a fatal validation rule defined in the ubl-2.1 specification. It validates the Character validation element in the UBL invoice XML.
When this rule fires, the invoice is rejected by Peppol access points and never reaches the buyer.
Target path: Character validation
Why This Error Matters
Invalid characters break XML parsing.
XML-004 is a hard failure — the invoice must be corrected and re-sent before it can reach the recipient.
Validator Behavior
- ·Causes invoice rejection
- ·Fails UBL schema validation
- ·Error returned: XML-004
- ·Specification: ubl-2.1
How to Fix It
Find invalid chars
Control characters, invalid Unicode
Remove or escape
Use XML entities for special chars
XML Example
Generic example based on the rule's target XPath. Your actual XML structure may differ.
<!-- Triggers validation error --> <Character validation></Character validation>
<!-- Corrected --> <Character validation>VALID_VALUE</Character validation>
Technical Reference
Character validationCommon Causes
- ·Control characters
- ·Null bytes
- ·Invalid Unicode
Seeing this in production? The API handles XML-004 automatically. See the fix response →
Frequently Asked Questions
Document contains invalid XML characters.
Remove or encode invalid characters. This error involves a protected field — Invoice Navigator flags it in your pipeline so your team can correct it at the source.
Yes, XML-004 is a critical error that must be fixed.
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Last updated: 3 March 2026
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