Rsync Task --link-dest=

[hsunhsun]

I want to bakcup my freenas to an synology by using the rsync.
I use the option --link-dest= and make Incremental Backup 3 days.
It's not work.

the rysncd.conf on synology nas

log file = /volume1/backup_freenas/rsyncd.log
pid file = /var/run/rsyncd.pid
lock file = /var/run/rsync.lock
use chroot = no

[backup_freenas_monday]
path = /volume1/backup_freenas/BackupNextcloud/MON/
uid = root
gid = root
use chroot = false
auth = Backup_freenas
secrets file = /etc/rsyncd.secrets
hosts allow = 192.168.1.61
read only = false

I create a folder on the synology. The Path:/volume1/backup_freenas/BackupNextcloud/FRI/.

The freenas rsync task extra option

--password-file=/mnt/Pool01/rsynctest/rsyncconfg/rsync.pwd --log-file=/mnt/Pool01/rsynctest/rsync.log --delete --link-dest=../../FRI

or

--password-file=/mnt/Pool01/rsynctest/rsyncconfg/rsync.pwd --log-file=/mnt/Pool01/rsynctest/rsync.log --delete --link-dest=../FRI

All the option make the log as follow:

2021/03/30 14:50:59 [15270] receiving file list
2021/03/30 14:50:59 [15270] --link-dest arg does not exist: FRI
2021/03/30 14:50:59 [15270] sent 75 bytes received 158 bytes total size 537917

Data is transmitted, but the --link-dest is not work.
Can anyone help me?
Thanks a lot.