When you use an inline script in a Flow, an error is thrown: fd_data is not defined

Data has to be accessed through the object fd_data but it needs to be in combination with fd_data.trigger.current:

If you just return fd_data you get 'fd_data is not defined', but if you use fd_data.trigger.current or fd_data.trigger.current.number you get valid data back.

Don't use fd_data on its own, it needs to be as follows: fd_data.trigger.current, or a similar construction.