Using third-party automated applications like SyncBackPro with Amazon S3 requires the use of special credentials called Access Key & Secret Key, which need to be obtained from Amazon direct (once you have an S3 account). You can currently access these via:
https://console.aws.amazon.com/iam/home?#/security_credential
After logging in, on the Access Keys tab, you'll find to the right of your active Access Key a link labeled "Show"...which when clicked will reveal your Secret key to you.
Note that direct cloud service functionality is a SyncBackPro-only feature.
