Note: This article has been updated with lastest available information on January 2nd, 2022 at 08:13 am
Anything you store on your app is linked to one specific device so unfortunately, it is not possible to sync tones across devices.
However, it is possible to create a backup of tones saved on your device, upload it to a Dropbox account and then download that backup from another device. This will allow you to sync Spark tones across all your devices. Check the tutorial on how to perform a tone backup from the Spark app.
Another option would be to upload all your tones to the ToneCloud. ToneCloud Tones and likes/favorites are linked to your profile, hence available on various devices with the same login.