SparkleShare sometimes has problems using the correct key for SSH authentication - especially if you already have installed and configured SSH and/or your Git client.
To make SparkleShare work, please ensure that all your SSH public keys (e.g. your original SSH key and the SparkleShare key) are registered within Planio.
You can find SparkleShare's public key in a file called 's link code.txt in the SparkleShare folder within your user folder.
Should you still have problems despite using the correct address (ssh://git``@[account].plan.io) and path (/[account]-[project].git), you could send us your SparkleShare logs so we can have a look.
The logs can be found by clicking on the SparkleShare icon in the menu bar, then on SparkleShare -> About SparkleShare -> bottom right Debug log.