FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
FortiOS 7.2.5 and 7.4 are using OpenSSL 3.0, in which x509 certificates signed using SHA1 are no longer allowed at security level 1 (the default level) and above.
To work around it, under 'vpn ssl settings', try 'set ssl-min-protocol to tls1-1', which will lower the security level to 0. However, this is strongly discouraged.
