FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Article Id 189810
This article will descibes how to communicate between two SSL clients connected on the same FortiGate.

Find the picture below, two hosts have been connected to the FortiGate using FortiClient.

The IP address of first client is while the second client has an IP
In order to make to communicate with, make sure the traffic reaches the FortiGate(enabling split tunnel is mandatory).
A proper policy is needed.

When client 1 ( wants to communicate with , the client forwards the traffic to FortiGate.
Go to VPN -> SSL VPN portals, edit the portal, enable the split tunnel and under routing address create an address object and the subnet

Add a policy.
Make sure the source interface and destination interface are SSL interface, next the source IP have subnet or on the number of client ) and user group and destination are the SSL VPN client IP.

As soon as the policies are made can communicate with