Can you run SNMPWalk against device and confirm if it responds to 18.104.22.168.22.214.171.124?
From your Orion server, open C:\Program Files (x86)\SolarWinds\Orion and run SNMPWalk.exe
- Enter IP address of Node, Community String
- Click Scan and then save the resulting text file to your desktop
Well, I should preface this with the fact that Fortinet's are evil! So that's probably a major reason why its not connecting. But, that being said...
Just configuring SNMP on a Fortinet isn't all you need to do to get SNMP working. You need to make sure that on the interface you want to connect to using SNMP, you have to check off the "SNMP" box for "Administrative Access". Just find it in the list of interfaces, probably by IP address, double click on it and once you're editing the interface it should be pretty apparent.
If you still have problems after that, its probably a firewall rule...