When you navigate to or Network > DDNS on a FortiGate (FortiOS 6.0 through 7.4), the firewall attempts to fetch an up-to-date list of supported DDNS providers (e.g., FortiGuardDDNS, no-ip, DynDNS, ChangeIP) from Fortinet’s FortiGuard servers.
Then restart the FortiGuard service: