Ember Serializer works for Mirage but not with real data

I am new to Ember and is trying to create a small application using version beta 2.3.0.

Provided a country and zipcode, I am trying to get the city and zipcode. With Mirage and a custom serializer (I am using the same format as of real json) my code works perfectly.

However, with the real API, the Promise remains in Pending state. There is no error in console. And the logs in my serializer does not display when using real service indicating that the serializer is not executing. Has anyone faced a similar issue before. Please help.