How to Connect an Ember app to a Rails API?

Currently having some trouble understanding how to connect an Ember app to a Rails API in my local dev environment. I'm pretty unfamiliar with this sort of set up, as opposed to just running a purely Rails application.

So run when I'm running these two separate apps, it looks like:

Ember app running on `localhost:4200`
Rails API running on `localhost:3000`

And both applications are in the same directory

Parent Directory
|
|___ API
|
|___ Ember App

When I visit both localhost URLs, both the apps are running. The Rails API seems to be fine, but the Ember app displays the default "There's something wrong" page that was made, and below is the error I receive in the console:

I was hoping someone could explain what might be wrong with my set up, that's causing this error.