Re: IP address conflict when setting up FortiGate 60E
I think you only need to change the "internal" or LAN IP subnet on the ISP router/gateway device and the DHCP settings handing out info to the CPE equipment (e.g. the fgt), this includes the DNS info.
If you are on site, connect your laptop directly to the ISP router/gateway device and see if you can browser/access the Internet - if not, troubleshoot accordingly.
Thing to watch out is a possible DNS related issue - trying pinging out both by FQDN and static IP (e.g. 22.214.171.124).
If your ISP router/gateway device can be placed into bridge mode: e.g. assigning the CPE a public IP then I suggest considering going that route - personal opinion though.
If the ISP router/gateway can not be placed into bridge mode, see if there are any firewall settings that would allow you to set up port forward or see there is already one on it. The port forward should be directed to the fgt's internal IP that is handed out by ISP router/gateway.
Not really needed, but it does help with troubleshooting is to set up DDNS setting on the fgt for the WAN(1/2) port.
NSE4/FMG-VM64/FortiAnalyzer-VM/6.0 (FWF30E/FW92D/FGT200D/FGT101E/FGT81E)/ FAP220B/221C