Backendless Service Platform is not just a mobile backend (mBaaS) - it also provides hosting and runtime support for browser-based applications.
To simplify the cross-origin setup, Backendless Console includes a special section where application developer can list all the host names 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:
The text field in the interface accepts the names of the hosts (domains) where a developer's JS app is loaded by a browser from. Enter the domain names or IP addresses (one per line) or use the * for all domains. Click Save to save the changes.