The Wohnungsgeberbestätigung (also called Einzugsbestätigung des Wohnungsgebers or Vermieterbescheinigung) is a document you get from your landlord, or the main tenant (Hauptmieter) in your WG, when you move in. It proves to the Bürgeramt that you live at this address.

When you register your address, you must have a Wohnungsgeberbestätigung. Without this document, you can't register your address.

The document below is an official example. You can use a different template, but it must contain the same information1.

The main tenant can sign this document, but only with the permission of the landlord1, 2. This means that you can't register a place as your official address without the permission of the landlord. This also means that you can't use a hotel or an AirBnB as your official address.

The landlord can't refuse to give you this document. The landlord can't refuse to let you register your address. You can read more about it here.