When you are setting up two FortiAuthenticator devices in active-passive HA, you need to select the active-passive master role on the master FortiAuthenticator device. This role means that the device will handle all requests and synchronize data with the slave device until a failover occurs. The slave device must be configured as an active-passive slave role. The other roles are used for different HA modes, such as standalone (no HA), cluster (active-active), or load balancing (active-active with load balancing). Reference: https://docs.fortinet.com/document/fortiauthenticator/6.4/administration-guide/372411/high-availability