The package for Synology NAS boxes is (or was, haven’t used it for quiet a while) using port 7070 and configured for external access (listens to 0.0.0.0).
If you did not change the config in any way, or it got corrupted for some reason, your way of accessing it should work.
I did not really use the package, because it had a really old version of Syncthing so I “installed” Syncthing manually. So I cannot really help you debugging the package. I described how I installed it here.