Under reverse charge (category AE) EN 16931 requires the Seller VAT identifier (BT-31, or tax registration BT-32) and the Buyer VAT identifier (BT-48) — so it is clear who owes the tax.
Add the Buyer VAT id (BT-48) and make sure the Seller carries BT-31 or BT-32.
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Rule source: EN 16931 / XRechnung (KOSIT) or Billhorse check (BH-*).