I have problem with sending COURSE to Fenix 5x (fw 9.71b) from GCM (4.8) - message "Your device does not support courses. ciq.forums.garmin.com/.../1370190.png
Searching the forums and the webber-tubes, seems that in most cases this was resolved by either what philipshambrook mentioned, and/or make sure Bluetooth is on and your device is connected to your phone. Then try to send the course again.