Troubleshooting Tip: Not possible to save admin-server-cert settings with HTTPS server certificate

A new SSL certificate was imported under FortiGate GUI -> System > Certificates, and it is shown as valid. However, it is not possible to save the system settings under FortiGate GUI -> System -> Settings with the new HTTPS server certificate.

An error message is displayed in FortiGate GUI: 'Administration settings failed to save: Input value is invalid'.

The new certificate is present under System -> Settings -> HTTPS Server Certificate. However, by checking the certificate via CLI, the certificate is not available to be used (the last entry should show the <certificate-name>).

config system global

    set admin-server-cert ?

Available Certificates:
self-sign local
Fortinet_Factory local
Fortinet_Factory_Backup local
Fortinet_GUI_Server local

To be possible to save the HTTPS server certificate settings, open the CLI and display the full configuration for the affected certificate:

config vpn certificate local

edit <certificate-name>

show full

Copy all the content of the CLI certificate configuration, as shown in the example below:

config vpn certificate local
   edit "certificate-name"
      set password ENC [ommited]
      set comments ''
      set private-key "-----BEGIN ENCRYPTED PRIVATE KEY-----
      [ommited]
      -----END ENCRYPTED PRIVATE KEY-----"
      set certificate "-----BEGIN CERTIFICATE-----
      [ommited]
      -----END CERTIFICATE-----"
      set range global
      set source user
      set source-ip 0.0.0.0
      set ike-localid-type asn1dn
      set enroll-protocol none
   next
end

Delete the new certificate under System -> Certificate, select the certificate, and select Delete. To re-import the certificate, paste the previously copied certificate commands into a new CLI window.

The SSL certificate should now be accessible as the HTTPS server certificate.

config system global

    set admin-server-cert ?

Available Certificates:
self-sign local
Fortinet_Factory local
Fortinet_Factory_Backup local
Fortinet_GUI_Server local

<certificate-name> local