DE-R-028
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-028
When both seller and buyer are located in Germany, the seller e-mail (BT-43) must contain exactly one @, not framed by whitespace or dots, with at least two characters on each side; a dot must not be the first or last character.
How to fix it
Fix the cbc:ElectronicMail value in the seller cac:Contact block.