Q&A: How many FortiManager licenses do you require for a FortiGate in a HA pair?

A: You'll only need to license for one device, including any VDOMs.

For example, we have 2x FG1000C's with 100 VDOMs in a HA pair.

The FortiManager will only need to be licensed for 100 devices as the HA pair count as one.