New User Can’t Connect (Gateway Timeout)

I’m a brand new user of UpdraftPlus and I’m trying to use it to make backups to a remote site via FTPS. However, when I set up and test the configuration I get the error message, “updraft_send_command: error: error (Gateway Timeout)”. The WordPress installation and plugin is on a local server under my control; the remote server is at a different site but is also under my control. I can connect to SFTP on the remote server (from outside the local network) using the same credentials I’m trying to set up in Updraft. I can also connect to and mount the remote server’s folder I’m trying to back up to on the local server via FTPS using the server’s administrative interface. What can I do to get Updraft to connect directly to the remote folder?