this.passthrough() functionality in Ember

I am writing an application in Ember.js and I am also using Ember mirage. I need to make requests to an external server and I am currently trying to set up my config.js file to deal with such requests. Adding this.passthrough() does not work and I still get an error when I try to make my request saying:

"Your Ember app tried to GET 'http://...' but there was no route defined to handle this request. Define a route that matches this path in your mirage/config.js file. Did you forget to add your namespace?

I believe this should be a simple thing to fix, any ideas of what is going wrong?