On a reverse-charge invoice the client's VAT-ID is required with no threshold
§ 11 Abs 1a UStG 1994 requires the recipient's VAT-ID on every invoice that shifts the tax liability — this provision knows no monetary threshold. The €10,000 threshold usually recalled sits in a different provision and concerns ordinary invoices with VAT shown. Stating the tax amount separately on such an invoice is expressly prohibited by the provision.