Change access proxy API gateway real server default port from 0 to 443.

config firewall access-proxy
    edit <name>
        set vip <string>
        config api-gateway
            edit <id>
                config realservers
                    edit <id>
                        set port <integer>
                    next
                end
            next
        end
    next
end

Where the port is a value from 1 - 65535 (default = 443).