DE-R-022
A Peppol Germany national rule (DE-R-*) – applies when the invoice is sent over the Peppol network to a receiver in Germany.
What this error means
DE-R-022
When both seller and buyer are located in Germany, attachment filenames (BG-24, BT-125) must be unique (case-insensitive).
How to fix it
Rename duplicate attachments in the cac:AdditionalDocumentReference blocks.