Just received an email stating :-
Airbnb-required security deposits
As part of our continuing effort to build trust on Airbnb, we may apply a security deposit for a small number of guests 48 hours before they check in. This is a limited test based on certain reservation details like timing and listing features.
No need to do anything—we’ll apply these security deposits automatically.
Thanks for hosting,
The Airbnb Team
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More about security deposits
Who decides the amount of the security deposit?
Since your listing doesn't have a security deposit set, if Airbnb applies a security deposit, the amount will automatically be calculated based on several factors, including the reservation total.
How do I collect from a security deposit?
You can report an incident and submit a claim within 14 days of check-out or before a new guest checks in.
To learn more about security deposits visit our Help Center.
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Note: If a security deposit hold can’t be authorized, the reservation will be subject to cancellation up to 36 hours before check-in. While Airbnb-required deposits are intended to protect our community, we are not responsible for failure to apply a deposit in any case where one may have been advisable.