Problem, sophos RED 15 cannot find sophos XG

I will test RED 15 with 2 firewall but I have some problem. My RED 15 can connect to router(firewall) but it cannot find XG(firewall that I add RED).

Firewall IP, I use public router(firewall) IP
RED IP, I use some private IP that it behind firewall.

and another firewall, I use it on other private IP.

My problem, RED cannot find SG115. LED on RED show blinking green light at "internet" ,and later, it reboot.

Thank,