I just started Syncthing today to sync my old Synology box to new FreeNAS and I love it already ! Simple setup !
One issue I cannot find in docs or forum is I want to sync a folder with my Time Machine backups. The folder is called “/volume1/Time Machine/” or /volume1/Time\ Machine/ on the synology. I have tried this format and quotes and quotes around “Time Machine”, but cannot get it to work. I always get folder does not exist.
Regardless, you should just enter it without any magic.
/volume1/Time Machine
However, FreeNAS does a lot of interesting things with process jails and permissions. Syncthing might just not be able to access the volume even though you entered it correctly.