Unable to choose port1 as ha-mgmt-interface while configuring HA

Hi,

So I have two FortiWeb 600D devices which I want to setup an Active-Passive cluster with.

Both are 'factory default'. I cleared the default IP from port1; But I'm unable to use it as a ha-mgmt-interface when configuring HA. All other ports are selectable.

Port config:

  config system interface     edit "port1"       set type physical       config  secondaryip       end     next

 (ha) # set ha-mgmt-interface  <datasource>    manager port interface  port2                system.interface  port3                system.interface  port4                system.interface  port7                system.interface  port8                system.interface

Hopefully someone has an idea?

KR,

Onno.