Here is the log when trying to backup sftp to a Nas.
[root@HHWESX2:/vmfs/volumes/587a1427-8aa8b904-a3ec-9c8e9926f41a] ./vertical backup Ubnt
Vertical Backup 0.3.1
Licensed to j****@***.com (Beta Testing); expires on 2018-02-13
vertical@192.168.0.8’s password (leave blank to choose public key authentication):
Storage set to sftp://vertical@192.168.0.8/Vertical
Listing all virtual machines
Backing up Ubnt, id: 4, vmx path: /vmfs/volumes/Datastore1/Ubnt/Ubnt.vmx,
guest os: ubuntu64Guest
No previous backup found
Virtual machine Ubnt is powered on
Removing all snapshots of Ubnt
Creating a new virtual machine snapshot for Ubnt
Uploaded file /vmfs/volumes/Datastore1/Ubnt/Ubnt.vmdk
Uploading file Ubnt-flat.vmdk
Uploading --------------------------------------------- 18.13MB/s 00:18:47 0.2%
Failed to create the directory ‘Vertical/chunks/be’: File already exists
[root@HHWESX2:/vmfs/volumes/587a1427-8aa8b904-a3ec-9c8e9926f41a]