After upgrading the firmware, I am unable to access to Fortigate using the UI (https)

Hi Jacky1,

It is possible to have access to the Secondary device's GUI/HTTPS by configuring a management interface under HA settings or configuring a management IP under the system interface

Connect to the slave FortiGate, proceed with the following command in the CLI:

execute ha manage <HA cluster index of the secondary unit> <username> <password>

And run the sniffer and debug logs and see the output result.

di de flow filter addr <src-address>
di de flow filter port 443
diag debug flow trace start 1000
diag debug en

Please refer to the below document for more information:

https://community.fortinet.com/t5/FortiGate/Troubleshooting-Tip-Unable-to-access-secondary-unit-GUI-in-HA/ta-p/363766

Regards,
Aman

Hi @Jacky1 ,

If you have no HA management interface configured, you can only access the current Primary Device in GUI.

Please share your HA settings.