Hi @Kolbrún2
This is not a fraudulent inquiry. Airbnb has been requiring hosts to provide them with updated personal information, when the company is preparing to hand over relevant, current host data to the local authorities (tax office, city councils etc), usually within the next 4 - 6 weeks. Invariably, the targeted hosts are lhosting in cities with upcoming or ongoing regulatory battles, long-term housing stock issues, and a recent strong upsurge in speculators, and commercial operators
As regards your registration number - if I recall correctly, hosts who rent over 90 days in Reykjavik are legally required to register with the city, in order to obtain a permit? Your permit or registration documents should have the number you need stamped on them.
Hope you get sorted. Best of luck!