Sorry, your upload failed. Register your device, and try again - importing fit files

Had to create a new Connect account and move the files there. I followed the official instructions and have a complete data export from my old account, which I was instructed to delete to be able to upload these files to the new account. However, I'm getting "Sorry, your upload failed. Register your device, and try again" for most of the files (I'm guessing the ones recorded by a previous watch). I no longer have the previous watch that recorded the activities because it stopped working. I tried running one of the fit files through a device changer and that did not work either. Any ideas for a workaround or am I completely out of luck?

  • Did you add at least one Garmin device to the new Connect account?

    Normally, unless something changed very recently, you do not have to register the device that the activity file you are trying to import was recorded with. Perhaps there could be some limitation at files with ECG or similar metrics, but I imported activities from 3rd persons just a few days ago, without any errors.

    If you dare zipping and posting a sample file here, we (me or other users) can try to import it and see whether we get the same error.