DE-R-017
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-017
When both seller and buyer are located in Germany, the invoice type code (BT-3) must be one of: 326, 380, 381, 384, 389, 875, 876, 877.
How to fix it
Change cbc:InvoiceTypeCode to an allowed code – usually 380 (invoice) or 381 (credit note).