DE-R-006
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-006
When both seller and buyer are located in Germany, the seller contact telephone (BT-42) must be provided.
How to fix it
Fill in cbc:Telephone in the seller cac:Contact block.