@Tobias_Wochinger Here it is:
The event order is for some reason wrong. The flight_departure_form should come before the slot events. I just tried this out myself and the order is definitely correct. How does your domain look like and which versions of Rasa Open Source and the Rasa SDK are you using?
the form slots that should be filled according to the domain file, were filled before a form validation was requested. In rasa 2.0, the form slots are empty. And when validation is asked from the action server, now the slot filling has to somehow happen in the actions server.
The slots should still be filled based on the slot mappings before the request is sent to the SDK. The SDK can 1) validate the extracted slots 2) Add new slot events (e.g. for custom slot mappings)