Hitman Pro 3.5.6 Error Code:20

Hello Gamers, Today I installed the Hitman Pro 3.5.6 and haven't been successful in going through. I got an activation error. I opened the firewall in my computer and I don’t know what to do next. Any solutions over there?
Hitman Pro 3.5.6- Build 108
An error occred during the activation process (error code:20). Firewall software on your computer might be blocking the hitmanPro35.exe application. Please update your firewall rules to trust this application
(full network access).
