In Veeam, when backing up linux-based VMs with application-aware processing turned on, testing the credentials may fail even though they have been entered correctly.

First, check whether you are really using linux-credentials and not Windows credentials, this can often be overlooked very quickly.

Check whether you see the logon attempt in linux. Depending on the distro, it is logged in a file in /var/log. E.g. for Debian/Ubuntu, it's logged in /var/log/auth.log. Looking at the logging will reveal whether it is a password or SSH key problem, or something else is going on.

Another possibility is that the required cipher is not allowed. Veeam requires the cipher aes128-cbc to be enabled. Alt  ...