Restrict sftp user to a single directory in El Capitan
Solution 1:
You need to make sure that the <the directory path> fulfils the next requirement specified in the manual pages for sshd_config(8):
All components of the pathname must be root-owned directories that are not writable by any other user or group.
If you don't, then
it doesn't work.
But you are certainly notified about the problem in system log.