I just discovered this a few days ago and used it last night ... worked for me.
Happy new year to the plotaroute.com staff.
Routes that I created yesterday and today (see links below) are not syncing to Garmin Connect. The start icon in 'My Routes' stays black and the routes don't appear in Garmin Connect.
https://www.plotaroute.com/route/2114538?units=km
https://www.plotaroute.com/route/2116537?units=km
Regards,
Winfried