Are you potentially trying to mount a SMB share to the root folder on your client (i.e. / )? The error looks like the client is attempting to do something it itself is not allowed on its machine. Try specifing a path to mount to which is writable - e.g. /tmp/mount (not that you should keep mounting there if it works).
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Is this Path option referring to the path on my android mobile? I thought it is referring to the path of my synology NAS.
Should I use exact path of android or relative path? I'm not quite sure what is the full path of my android mobile. But I think it is something like ...emulated/0/...
I think its you device‘s path, i.e. on Android - otherwise the error would look different I presume.
Yes, /emulated/0/my-smb-mount or similar looks about right.
You may need to include a path. You might need to add each of your Shared folders separately. I have had this issue with Samba before where the host was browseable, but you could not mount the whole server.