For a cancelation to sync to Guesty, Guesty should remain your listing's connectivity provider on Booking.com. If Guesty is no longer listed as the listing's connectivity provider, cancelations will not sync to Guesty.
Also, when linking a Booking.com listing to Guesty, we import your existing reservations in a Non-XML format. Any change you make to the reservation, including canceling it, won't sync to Guesty.
In both cases, contact us to cancel the reservation.