Red Hat 3scale API Management returns "Application is not available" when attempting to access the Admin Portal

Issue

When accessing the Admin Portal, the following OpenShift message is displayed:

Application is not available
The application is currently not serving requests at this endpoint. It may not have been started or is still starting.

Possible reasons you are seeing this page:

The host doesn't exist. Make sure the hostname was typed correctly and that a route matching this hostname exists.
The host exists, but doesn't have a matching path. Check if the URL path was typed correctly and that the route was created using the desired path.
Route and path matches, but all pods are down. Make sure that the resources exposed by this route (pods, services, deployment configs, etc) have at least one pod running.