Whenever you receive a HTTP error (4XX or 5XX) we recommend you use the CheckBookingStatus method to check if the booking exists.
The return of this method will be the Booking Id and Service Id or an error.
If you receive an error you can try to call the doBooking method to make the booking.
If you receive the Booking Id and Service Id you have to use the ClientBackoffice API to get the booking details and check the booking status.