"Can’t download firmware from Fortinet—contract expired." Fix: Fortinet Support will often provide the last EOL build for free if you open a ticket citing "Security remediation for legacy hardware." It is not guaranteed, but it is worth a try.
If you still operate a FortiGate 100D:
You should only download firmware from the official Fortinet Support Portal to ensure file integrity and security. Fortigate 100D Best & Latest stable firmware Fortigate 100d Firmware Download BEST
Go to System > Dashboard > Status and click Backup . "Can’t download firmware from Fortinet—contract expired