Please follow the steps and verify if issue persist:
1.In order to upload audio files to the host after RUTX11 through FTP connection, RUTX11 should has public IP assigned by SIM service provider.
2.Verify port forward configuration in RUTX11. You may configure external port 21 or other unreserved ports (the port number being used in FileZilla for establishing connection to the host) and configure host LAN IP with internal port 21 for redirect connection.
3.Ensure host has port 21 opened and no firewall rules has denied FTP connection.
4.Ensure host IP, port and login credentials have been correctly entered in FileZilla.
If issue persist, please download troubleshoot file via RUTX11 WebUI-System-Admin-Troubleshoot then send me the file through private message.