An invoice meets the formal requirements if it contains the following points:

• Name and address of the supplier and his company identification number (UID)
• Recipient’s name and address
• Delivery date (if not identical with the invoice date)
• Exact description of the service
• The price of the service
• Amount of VAT applied
• advanced digital signature for PDF invoices

Detailed information under: Bundes im KMU-Portal (in German)