The log viewer within the portal can be used to see supplier logging, and reasons for failure.
There's also a booking retrieve call in the API that gives you headline data about the booking, iVectorOne API log data as well as the supplier API log data all in one place.
The call takes 3 parameters:
Booking Reference - e.g. the BookingReference field you have passed in at book
Supplier Booking Reference - the reference that the supplier returns in the book response, providing that the book response is successful. If the book request was not successful, then the value of this parameter will be "failed"
Supplier - the name of the supplier that the booking was made with
For example, if the booking ref passed was A, the supplier was ATI and the booking failed, the parameters would be
if the booking ref passed was B, the supplier was ATI and the booking was successful - ATI returned the reference ABC123, the parameters would be