pfSense

site-to-site.

if set in openvpn client option "remote network" for example "192.168.18.0/24" -- openvpn client is crashed with parsing error.
For remobe this error need only(!) reboot server.

If need site-to-site routing - add command "route 192.168.18.0 255.255.255.0 192.168.220.9" (220.9 - is gateway ip in tunnel)

in log:

Jul 16 15:24:40 openvpn 36285 OpenVPN 2.4.4 amd64-portbld-freebsd11.1 [SSL (OpenSSL)] [LZO] [LZ4] [MH/RECVDA] [AEAD] built on Mar 16 2018
Jul 16 15:24:40 openvpn 36285 library versions: OpenSSL 1.0.2m-freebsd 2 Nov 2017, LZO 2.10
Jul 16 15:24:40 openvpn 36354 NOTE: the current --script-security setting may allow this configuration to call user-defined scripts
Jul 16 15:24:40 openvpn 36354 OpenVPN ROUTE: OpenVPN needs a gateway parameter for a --route option and no default was specified by either --route-gateway or --ifconfig options
Jul 16 15:24:40 openvpn 36354 OpenVPN ROUTE: failed to parse/resolve route for host/network: 192.168.18.0
Jul 16 15:24:40 openvpn 36354 TUN/TAP device ovpnc3 exists previously, keep at program end
Jul 16 15:24:40 openvpn 36354 TUN/TAP device /dev/tap3 opened
Jul 16 15:24:40 openvpn 36354 do_ifconfig, tt->did_ifconfig_ipv6_setup=0
Jul 16 15:24:40 openvpn 36354 /sbin/ifconfig ovpnc3 192.168.220.10 netmask 255.255.255.252 mtu 1500 up
Jul 16 15:24:40 openvpn 36354 /usr/local/sbin/ovpn-linkup ovpnc3 1500 1592 192.168.220.10 255.255.255.252 init
Jul 16 15:24:40 openvpn 36354 TCP/UDP: Preserving recently used remote address: [AF_INET]66.166.98.26:1196