'Could not create directory'

Ok, so I am trying to install plugins on my wordpress site, and when I tried my first one wordpress said it needed FTP details. Specifically, the hostname, ftp username, and the ftp password. On my server, the whole wordpress site is under a directory, and I have made a new ftp user, and given it all permissions over that whole directory. Any idea why when I try to download a plugin in says this? – “Unpacking the package…

Could not create directory.”

Thanks!