By default, the 80 and 443 port is used to provide web service and reverse proxy service.
In this case, you are not allowed to use these ports in the proxy service.
Starting to v2.09.061512 your are allowed to unlock this limitation using this way
- On the TOP menu , choose “Your Proxy” icon
- Select “Listen Ports” link
- Select Port 80/443 button
- Turn to green the feature and click on Apply