fatalPeppol BIS Billing 3.0profileUBLBT-10
The element "Buyer reference" (BT-10) shall be provided.
The Buyer reference (BT-10) is missing. In Germany this carries the Leitweg-ID, the routing identifier of the public authority you are invoicing - without it the invoice cannot be delivered.
Add BT-10 (UBL cbc:BuyerReference). For a public-sector buyer this must be the Leitweg-ID they gave you, in the form 991-12345-67. It is not a free-text order reference: if you invent one, the invoice is technically valid and still undeliverable. Ask the authority for it.
UBL — context (/ubl-invoice:Invoice | /ubl-creditnote:CreditNote)[$supplierCountryIsDE and $customerCountryIsDE]
cbc:BuyerReference[boolean(normalize-space(.))]