Please review the thread linked below and provide us with the updated information about your particular issue:
Guide To Opening An Effective Forums Thread
Thank you.
My issue is identical to the one reported by the OP. Specifically, I am using the WHM backup (not legacy) to create backups, with the idea to transfer them securely to a remote location for safekeeping, as required to have a reasonably safe backup protocol in place.
When attempting to "validate" the remote location using the WHM backup configuration, the cPanel server successfully connects with the remote server, but is unable to complete the validation, returning an error message:
Error: Validation for transport “Adrive SFTP” failed: Could not upload test file: Couldn't open remote file '/validate.tmp-13869-1458784036.txt': Permission denied
I am attempting to transfer to my account at Adrive.com, which is configured for SFTP, and to which I have been able to successfully transfer backups from WHM cPanel using regular FTP. I had trouble connecting using password authentication, but as Adrive supports key authentication, I used that and connected successfully, but unable to "validate" so that WHM would begin to use the Adrive for backup storage.
I've consulted with Adrive support about this, and after investigating, they referred me to this thread, indicating that it is a cPanel bug.