How to fix PDF-17
The XMP does not declare PDF/A-3
A check of the PDF of a ZUGFeRD or Factur-X invoice, not of its XML. It runs when you upload a PDF; the embedded XML then gets the XSD and EN 16931 checks (XRechnung: also the KoSIT rules). Check your PDF with the ZUGFeRD validator or the Factur-X validator. What the PDF check covers.
PDF/A-3 (basic check). This is one of a few basic PDF/A checks. They are not a full PDF/A validation: rules such as CIDSet, transparency or tagged structure are not checked. For a full PDF/A-3 check, run the PDF through veraPDF.
What this rule checks
ZUGFeRD and Factur-X are PDF/A-3 files: the XMP must have pdfaid:part 3 and pdfaid:conformance A, B or U. Only PDF/A-3 allows embedded XML files. This checks the declaration only, not that the PDF meets PDF/A-3.
How to fix it
Create the PDF as PDF/A-3 (for example PDF/A-3b) with a tool that writes the PDF/A identification.
Related rules
Validate your invoice
Upload your corrected invoice to check it passes PDF-17 and all other ZUGFeRD / Factur-X PDF checks and EN 16931 rules. Free, instant, no signup.