Not able to use SFTP

Rsync.run("/home/user/folder", "sftp://user@hostname.net:/home/user/")
=># <Rsync::Result:0x00000000f02c10 @raw="ssh: Could not resolve hostname sftp: Name or service not known\r\nrsync: connection unexpectedly closed (0 bytes received so far) [sender]\nrsync error: unexplained error (code 255) at io.c(226) [sender=3.1.1]\n", @exitcode=255>
