I have a bunch of courses I've created in Garmin Explorer. I've exported to a GPX file and tried to import to Connect but it fails. "Your course cannot be imported. Something is wrong with this file." I'd think that two Garmin software apps would be compatible with one another.
It sounds like you're trying to import as an activity. Make sure you're using the import course link from the courses page on Garmin Connect.
Go to your courses page - https://connect.garmin.com/modern/courses
Click on Import
Drop the downloaded gpx file onto the Import Courses window
Follow the prompts to complete the setup.
