Permission denied when add folder

Hi all.

Can someone who has successfully implemented SyncThing on Truenas Scale and Qnap with me? I was able to install Syncthing and follow the instructions on the datasets in truenas but when I'm trying to add the folder to sync, I keep getting Permission denied at /mnt/Data even though the directory is located somewhere else. I have changed the directory setting according to some of the solutions that I found to /mnt/Data and haven't had any luck. All I'm trying to do is syncing data from my Qnap -> Truenas directory and both of them are giving me the same Permission error. I keep seeing people having the same issue but no solution is provided. Would anyone be able to chime in and share some steps to make it work? Appreciate it.