For SFTP you must use the according SFTP type in the External account settings (in Administration/Platform/External accounts).
So it will generate the sftp:// protocol in the activity logs; you should use the debug log checkbox in the Transfer file activity to verify it.
Please don't mislead with FTP with SSL protocol, ftps://, that is an old way to secure connection but not so secure by now so please forget it; FYI it is managed through External account FTP type, and by selecting SSL security in listbox. But I am quite sure you must NOT use that way.
Because your logs mention sftps:// wrong syntax, I wonder if you wrote this code by calling JSAPI and not through workflow activity Transfer file ?