Tested on FortiOS 5.6.7

Create Admin Profile

Go to the Admin Profiles menu and create a new admin profile (REST Profile) as below:

Set Up FortiGate Account

Select the account type as API Key and configure the Trusted Host range to include the Logpresso IP.

Set Up Connect Profile

Go to Settings > Connect Profiles and click the Add button. Set the profile name, identifier and the details as below: