Cannot save sync.ffs_lock on TrueNAS SMB share drive

[premium_user]

I have TrueNAS-SCALE-24.04.2.2 and SMb share to access files fom Windows.
I've been using FreeFileSync and loving it so much that even paid for it twice to support development.
The sad thing is that when I tried to sync local folder with my NAS, FFS GUI cannot save "sync.ffs_lock" on the SMB share location to start sync.
User creds which I use to access SMB from Windows has Full Access via ACL attached to a group (which this user belongs to).
Anyone has an idea what can I do to be able to use FFS?
Thanks in advance for all help.

--- ERROR example: ---

Cannot set directory locks for the following folders:

Cannot write file "\\TRUENAS\shared-data-pool\photos_sorted\sync.ffs_lock".
ERROR_ACCESS_DENIED: Access is denied. [CreateFile]