So I went to this [guide](http://bit.ly/qStKqp) that explains how to start with omniauth. When I got to the end of step 4 to test the application at localhost:3000/auth/facebook, I got this error:

```
{ 
    "error": {
        "message": "Invalid redirect_uri: Given URL is not allowed by the application configuration.",
        "type": "OAuthException",
        "code": 191
    }
}  

```

I understand the problem is the URL in the Facebook developer center, but none of the solutions I read works for me...

(I know that there are some questions before regarding this issue, but I'm new to Ruby on Rails and need an explanation for dummies.)