BR-DE-17:Seller contact information (name, phone, email) required in XRechnung

Fix: Step 1: Locate cac:AccountingSupplierParty/cac:Party in the Invoice or CreditNote. Step 2: Make sure a cac:Contact child exists. If not, create one — its position is after cac:PartyTaxScheme and before cac:PartyLegalEntity in UBL 2.1 canonical order. Step 3: Populate the three required children: • `<cbc:Name>Accounts Receivable</cbc:Name>` — a department, role or person name (BT-41). • `<cbc:Telephone>+49 30 1234567</cbc:Telephone>` — a usable phone number, with country code recommended (BT-42). • `<cbc:ElectronicMail>invoicing@example.de</cbc:ElectronicMail>` — a monitored email address (BT-43). Step 4: Validate each value: • Name must be a non-empty string with no leading/trailing whitespace. • Telephone should be at least 5 characters; many validators accept any digits and `+ - ( ) space` but reject letters. • Email must contain exactly one `@`, a non-empty local part and a domain with at least one dot. Use a deliverable address — the buyer's accounts payable team uses it to query the invoice. Step 5: Do not put contact data under cac:PartyContact (deprecated). The KoSIT validator only checks cac:Contact. Step 6: Re-validate against the KoSIT XRechnung 2.x or 3.x ruleset. BR-DE-17 should clear, and BR-DE-18 (cbc:ElectronicMail required) and BR-DE-19 (cbc:Telephone required) — its sibling rules — should also pass. Provide the required value in the free validator.

BR-DE-17 fires when an XRechnung invoice's seller party (cac:AccountingSupplierParty/cac:Party) does not carry a complete cac:Contact block containing the seller contact point name (BT-41, cbc:Name), telephone (BT-42, cbc:Telephone) and email (BT-43, cbc:ElectronicMail). XRechnung makes all three contact fields mandatory; Peppol BIS Billing 3.0 makes them optional, so an invoice that validates against Peppol can still fail KoSIT XRechnung validation with BR-DE-17.