I've a jailed user "ftest" (in /home/ftest) but he can't create files or folders within the jail.
User was added by:
useradd -g nginx -G sftpjail -s /bin/false
Permissions and owners are:
755 root:sftpjail /home/ftest 755 ftest:nginx /home/ftest/test1 755 ftest:sftpjail /home/ftest/test2 777 ftest:nginx /home/ftest/test3
The chroot sftp login is working just fine, but unfortunately it's not possible to write to any of the testX folders.