All services (nginx, varnish and apache) are installed and running. Therefore you need to dig logs to identify why you get the error 403. I recommend you to do following:
1. Create some test .html file and place it in the document root of the website
2. Create a test script .php and place it in the document root of the website too
3. Try to open the .html file over
http://domain.com/test.htmlif there is no error then the problem is caused by Varnish or Apache. In other case it means access is blocked by Nginx (check logs to get more info about the problem, review the nginx config file of the virtual host)
Do step 4 if the step 3 was accomplished without the error.
4. Try to open the .php script over
http://domain.com/test.phpand check the logs to get more info about the problem. Look for the records associated with your WAN IP and your test script.