When using a Hezner storage server as an Additional Backup destination, the validation check will complete, but backup transports fail when backups are run:
[20XX-01-01 00:00:00 +0000] info [cpbackup_transporter] Upload attempt #2 starting for /backup/weekly/20XX-01-01/accounts/username
to remote/weekly/20XX-01-01/accounts/username for destination: HetznerBox
[20XX-01-01 00:00:00 +0000] warn [cpbackup_transporter] Upload attempt failed: child exited with code 1
Heztner can be set up as a rsync destination and will validate successfully using their implementation of rsync. However, their implementation is limited by design and does not function as a full shell. The cPanel's backup transporter requires full shell privileges to successfully upload, track, and validate the completed transport backups.
Heztner servers can be used as an FTP destination instead.