Replication Task Fails with SSH Authentication Error on TrueNAS

I’ve been encountering an issue while trying to set up a replication task from my TrueNAS server to an external Rsync.net server using SSH. Despite being able to manually SSH into the Rsync.net server without any issues, the replication task continues to fail with an authentication error.

System Information:
TrueNAS Version: TrueNAS-13.0-U6.2
Replication Task Source: /mnt/DATA1/BACKUP
Replication Task Destination: /mnt/data1/BACKUP on Rsync.net
Transport: SSH
SSH Host: de1072b.rsync.net
SSH Connection: Configured manually with a private key at /root/.ssh/id_rsa

User: root
Error Log:
[2024/09/06 11:29:03] INFO [Thread-5] [zettarepl.paramiko.replication_task__task_1] Connected (version 2.0, client OpenSSH_7.9)
[2024/09/06 11:29:03] INFO [Thread-5] [zettarepl.paramiko.replication_task__task_1] Authentication (publickey) failed.
[2024/09/06 11:29:03] ERROR [replication_task__task_1] [zettarepl.replication.run] For task ‘task_1’ non-recoverable replication error ReplicationError(‘Authentication failed.’)

What I’ve Tried:
Manual SSH Test:
I can manually SSH into the Rsync.net server from TrueNAS using:
ssh -i /root/.ssh/id_rsa root@de1072b.rsync.net
The connection works without any password prompts.

Correct Key:
The public key is uploaded to the Rsync.net server’s ~/.ssh/authorized_keys file, and the private key is stored in the TrueNAS /root/.ssh/id_rsa. The permissions on .ssh and authorized_keys are correct.

Host Key:
I’ve used the correct host key discovered via TrueNAS and verified it matches the Rsync.net server’s fingerprint.

SSH Connection:
I’ve created a new SSH connection in TrueNAS and assigned it to the replication task, with the same failure happening.

Questions:

Has anyone experienced similar issues with replication failing on SSH public key authentication?
Are there specific settings in TrueNAS I should double-check when creating the SSH connection for replication tasks?
Could this be related to the version of SSH (OpenSSH 7.9) that TrueNAS is using?
Any help or insight from the community would be greatly appreciated. I’ve already reached out to Rsync.net support, and they’ve confirmed the key is correctly uploaded on their side.