I am new to Sublime Text, and have not worked with local web server very often, so perhaps the solution to this is really obvious, but I am having problems.

I am trying to open a project that uses the Phaser game framework, which requires a web server. Previously I had been copying it into the web server’s www directory when testing, and testing on localhost, but this is a pain to do. After doing a bit of research I found out about SideBarEnhancements, and tried to follow this guide:
hongkiat.com/blog/preview-in-localhost/

I opened sidebarenhancements.json and added this:

   {
        "C:/Users/Travis/Documents/Development/WebDevelopment/phaser-coding-tips/issue-001":
        {
            "url_testing": "http://localhost/"
            , "url_production": "http://someserver.net"
        }
    }

But when I tried to open it using the testing url, it tells me the file is not found, giving a standard 404 Not Found error:

Is there something else I have to do in order to set this up?