Can not Trigger Failover for configuration of remote IP monitoring

Hi all, 

I am using FortiWifi 60D and I need to monitor the link state of the "LAN" connection. Since "LAN" is not physical and cannot be monitored by cmd "set monitor xxx", I use another way link-monitor to trigger the failover by means of monitoring the IP address of the connected server in "LAN" side.

However, when the server IP cannot IP, the failover did not happen. And the configuration of link monitor was set as below:

Config system link-monitor

           edit "internal-link-monitor"

                     set srcintf "lan"

                     set server "192.168.1.200"

                     set failtime 3

                     set ha-rpiority 40

             next

end

Config system ha

            set group-name "HA-Group"

            set mode a-p

            set session-pickup enable

            set override disable

            set priority 150

            set monitor "wan1"

            set pingserver-monitor-interface "lan" "internal"

            set pingserver-failover-threshold 2

            set pingserver-slave-force-reset disable

end