Hello @Mhéo 

Sorry to hear you're getting a duplicate activity error when  attempting to upload a file.  The first thing to check is to make sure the activity you are attempting to upload has not already uploaded to your Strava account.  For example if there is a delay with a Garmin activity syncing to your Strava account, you may attempt to upload the Garmin file directly as a workaround.  However if Garmin has synced that activity in the meantime, you will encounter that duplicate error.

Another thing to check:   Did you use another device or platform to record the same activity?  If, for example, you have uploaded an activity from Zwift, or Apple Watch, and then attempt to upload the same activity from Garmin, you will get a duplicate upload error.  

If you still need help, please submit a support ticket and we’ll be happy to investigate further.