How to open a .fit file (a structured workout, not a course) on my Garmin Connect app?

I’ve been using the Garmin FIT SDK to create custom .fit files, specifically intended as running interval workouts. However, when I open the .fit file on my iPhone and choose to open it with the Garmin Connect app, it automatically gets imported as a course instead of a workout.

I've followed the documentation for making a workout activity and ensured the format is correct.

Is this simply not the way to get a .fit workout into my watch? 

Thanks in advance!