Here what they were told. I even tried sending a special offer and pre-approving... they are over the age of 25...
Your reservation couldn't be made.
We have implemented restrictions that prevent guests from making reservations for entire homes or private rooms when a pattern of factors suggest that the booking may present higher safety risks (such as parties).
While we know this may be an inconvenience you still have options. These restrictions dont apply to hotels.
Sorry to hear you lost the booking. In future, if you trust the guest and feel comfortable taking the booking, try temporarily changing your settings from Entire Home to Private Room. Failing that, try getting your guests to book for different dates, and you can amend afterwards. It's a bit of faffing around, but very few of us can afford to be losing bookings after the year we've had. Also, if you haven't done so already, look into listing on other sites too, in case this happens again.