Re: IPSec Tunnel Won't connect to remote fortigate
You showed policy with destination interface 'internal'. If the resource is accessible via different interface you need a separate policy.
Selectors - this is how you define what traffic should be sent to the tunnel. If you specify destination for example 10.0.0.0/24, you can't send traffic to 10.1.0.0/24. Verify your VPN settings (phase2).