networking - Write Permissions denied to LAN mounted drive

16.04 attempting to rsync with a LAN connected Western Digital Mycloud NAS. CIFS utilities installed to 16.04:

sudo apt install cifs-utils

Mounted remote NAS to /mnt/nas :

mount -t cifs //192.168.8.XXX/Public -o username=root,password=secret /mnt/NAS

Successfully listed (read) the contents of /mnt/NAS :

ls /mnt/NAS/Azimuth_Backup/

SYMPTOM: unable to write to the NAS from 16.04:

touch /mnt/NAS/text.txt

touch: cannot touch '/mnt/NAS/text.txt': Permission denied

mount details :

 mount | grep -i Public

//192.168.8.XXX/Public on /mnt/NAS type cifs (rw,relatime,vers=1.0,cache=strict,username=root,domain=NAS4TB,uid=0,noforceuid,gid=0,noforcegid,addr=192.168.8.XXX,file_mode=0755,dir_mode=0755,nounix,serverino,mapposix,rsize=61440,wsize=65536,actimeo=1)

If the cifs device is mounted with superuser / root, why am I unable to write to the remote NAS disk? Any examples that solve the issue or sharpen the question are appreciated.

It seems that root is the owner and write permissions are enabled:

ls -l /mnt/NAS | grep -i backup

drwxr-xr-x 2 root root 0 Nov 12 23:19 Backup