I've already tested the Flight Inspiration Search on test mode and worked fine with the restricted data, so I've decided to move to live with the API. Anyway, it looks like I'm still getting restricted data, because I've got errors (code 500 - not supported origin and destination) for airports like JFK, LTN, etc.
I've changed the base URL and the credentials, so it should retrieve the proper data. Do you have any suggestions for this?
The Flight Inspiration Search API is built on top of a pre-computed cache this is why, even in production, you don't return all possible options. The API computes every day the most trending options based on past searches and bookings and fills the cache, which means that the cache is dynamic. That's why you don't return anything with your defined criteria.
For real-time data you should use the Flight Offers Search API.