Did you follow the instructions in the get-started link? See below instruction snippet:

Now this is the command to fetch all information in the bridge. You didn’t get much back and that’s because you’re using an unauthorized username “newdeveloper”.

We need to use the randomly generated username that the bridge creates for you. Fill in the info below and press the POST button.

URL/apiBody{"devicetype":"my_hue_app#iphone peter"}MethodPOST

This command is basically saying please create a new resource inside /api (where usernames sit) with the following properties.

When you press the POST button you should get back an error message letting you know that you have to press the link button. This is our security step so that only apps you want to control your lights can. By pressing the button we prove that the user has physical access to the bridge.