The Flight Api Works perfectly, The only problem is during the search the section Flying from is not selected automatically when you choose the round trip, which is why you are getting that error. After changing it to roundtrip make sure that you select the place for the flying from again. If it does not change the flight modules to Amadeus everything will work perfectly. Remember the duffel flight API is for demo purposes
Create an Account for the API modules you want to use and see everything will be working fine
Am here to help if you need a developer to fix things for you...
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