Trouble with rsync syncing from OS X Sierra to Windows Server 2012 share

First post - sorry if I'm putting this in the wrong community.

This seems like an easy question, but I must be missing something obvious...

I'm trying to write a backup script for a few Macs in our environment. The script is supposed to:

1. Connect to the user's private folder (located in our network on a Windows Server 2012 share)

2. Sync stuff from the user's desktop and documents folder into 2 folders on the share - 'backups-desktop' and 'backups-documents'

Here are the pertinent parts of the script:

umount /volumes/username [some of the users already have their share mounted, so this makes sure I don't mount it a second time, which causes problems]

open smb://network-share-location

sleep 5

rsync -aE --delete /Users/username/Desktop/ /Volumes/username/backups-desktop

rsync -aE --delete /Users/username/Documents/ /Volumes/username/backups-documents

When I run the script I get a bunch of "permission denied (13)" error messages. None of the files are able to sync, only empty folders.

It doesn't seem to be a permissions error - the user has R/W permission for the share folders on the Mac side, and everything except for 'Full Control' on the Windows side.

Also, when I log into the Mac as the user I don't have any issues manually connecting to the network share and copying files from the Mac into the share... it's just when I try to run rsync that it has issues.

Thanks for any help.