Did you only change the URL from http://127.0.0.1:8384/ to http://x.x.x.x:8384/? (where x.x.x.x is your private IP address).
If so, there’s an additional required step. In Syncthing’s web UI, click Actions → Settings → GUI and update the address and port number Syncthing should use. For more details, see Syncthing’s documentation: The GUI Listen Address
And for additional tips and security considerations, just a few of the earlier forum threads:
- https://forum.syncthing.net/t/accessing-server-from-desktop-computer/16608
- https://forum.syncthing.net/t/how-to-access-gui-on-linux-centos-remotely/16831
- https://forum.syncthing.net/t/ssh-webgui-forwarding-headless-server/18680
- https://forum.syncthing.net/t/syncthing-gui-address-0-0-0-0-8384-with-a-password/20271