You must access Windows Server and enter regedit
Go to the path : HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\FlexFirewall
Create the named string "Log.BlockActions" and add the number 1 as content value
REG ADD "HKLM\SOFTWARE\Wow6432Node\FlexFirewall" /f /v "Log.BlockActions" /t REG_SZ /d "1"
To disable it change the 1 to 0 or delete the record
You will find the panel.ini file at:
%plesk_dir%admin\conf\panel.ini
Add the following code at the end
[ext-flex-firewall-manager] Log.BlockActions=1;
Flex Firewall Manager checks for changes in panel.ini every 2 minutes