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"This is a ChrootDirectory ownership problem. sshd will reject SFTP connections to accounts that are set to chroot into any directory that has ownership/permissions that sshd considers insecure. sshd's strict ownership/permissions requirements dictate that every directory in the chroot path must be owned by root and only writable by the owner. So, for example, if the chroot environment is /home must be owned by root. " see https://wiki.archlinux.org/index.php/SFTP_chroot
If you just enable it and create the group with a user then it is not working, because of the wrong ownership. Just to provide the user a hint.