Symptoms
SFTP Backup extension fails to connect:
Failed to create the directory "example" at example.com: unable to make SSH connection: ssh: handshake failed: ssh: unsupported DSA key size 2048
Cause
This is caused by the product issue EXTPLESK-5635, which will be fixed in a future version of the extension.
Resolution
Consider using an alternative backup method if possible.
As a workaround, the directory /var/lib/psa/dumps (which contains local backups) can be backed up manually with the rsync utility, or similar.