The message suggests that there is a DNS level problem with the FTP connection. Your computer tries to look up the FTP hostname, but gets no result.
The correct FTP hostname to use is ftpupload.net. If that one doesn’t work, you could also try to use ftp.infinityfree.com as FTP hostname instead. And if that also doesn’t work, you could try entering the IP address 185.27.134.11 directly.