What is W-IdNr.?
The Wirtschafts-Identifikationsnummer (W-IdNr.) is a nationwide ID for economic actors in Germany. Rollout and invoice duties are evolving — check current BMF / tax-office guidance.
Do not confuse it with the Steuernummer or USt-IdNr. Until your case is clear, keep existing required fields correct and watch ELSTER / adviser updates.
General information only — not legal or tax advice. Tax and e-invoice rules can change; the applicable laws control (e.g. § 19 UStG, § 14 UStG). Confirm with a tax advisor or lawyer if unsure.