Deploying and configuring FortiGate-VM active-active HA
See GitHub for details on this configuration. Although GitHub only refers to 6.0, you can deploy this HA configuration for 6.4.
Network Security 
Network Security
NOC & SOC Management
Enterprise Networking
Business Communications
Zero Trust Access 
Cloud Security 
Hybrid Cloud Security
Cloud Native Protection
Web Application / API Protection
SAAS Security
Security Operations 
SOC Platform
Advanced Threat Protection
Endpoint Security