Booking by API : Document the behavior of a carpooling operator that denies a booking request.

[pierrecamilleri]

I wonder what Response a carpooling operator should return, in case of a POST /bookings request, when he wants to deny the booking (for instance, if the Journey is no longer available), and I think it should be documented.

I am not sure about the best way to deal with this, I may suggest to use the HTTP Status code "409 Conflict" with an error message, as the main use case I see is that the resources have changed on the carpooling operator side between the search and the booking requests.