Hello, according to the information received by Airbnb this number must be applied to the listings wiithin the European Union.
The German translation would be Grundbuchblattnummer. I only found a Grundbuchnummer being the same as the Katastralgemeinde number on the Land registry sheet / Grundbuchauszug. I asked lawyers, accountants, department of finance and tourism and of course the Airbnb support. No one seems to know whiich number exactly is meant in the Austrian system. Anyone has solved this riddle by now? Thank you, Paul