Some cities require Hosts to obtain a license or registration number to list their places on Airbnb. The corresponding field on their listing allows them to show that number for compliance.
Not every city requires this, so the absence of a registration number does not mean the Host is not compliant—they’re just not required to register.
Instead of number, you might find another message in that field:
In rare cases, a Host might abuse this field on their listing by entering a phone number or an email address, encouraging you to contact them directly to book outside of Airbnb. Don’t fall for it—remember: If you transact off the Airbnb platform, you will not be protected under our Terms of Service, cancellation and refund policies, Host Guarantee, Host Protection Insurance program, and other safeguards.
If someone asks you to do this—or you think someone might be abusing this field—let us know and click the flag icon to report the listing.