Unless you host your Backendless-powered app in our hosting system, you will be running into cross-origin domain requests. This occurs when an application is loaded into a browser from one host, but then it makes a request (XHR, socket, etc) to another host. In the case of Backendless, the second host would be the backend platform we provide.
To simplify the cross-origin setup, Backendless Console includes a special section where an application developer can list all the hostnames where the app may be loaded from. You can access that section on the Manage > App Settings screen and then scroll down to the Domain Control section: