App Engine app needs to publish and subscribe to Cloud Pub/Sub but the Pub/Sub API is currently disabled. Using a service account for authentication, what should you do to allow the app to use Pub/Sub?

To use any Google Cloud API, including Cloud Pub/Sub, you must explicitly enable it for your project. This is a fundamental security and resource management step. The Cloud Console's API Library provides the interface to enable or disable APIs. Assuming the API is enabled automatically is incorrect; explicit enablement is always required. While Deployment Manager can automate infrastructure, it doesn't automatically enable APIs that are not explicitly configured for enablement within the deployment. Granting a service account roles like "Cloud Pub/Sub Admin" provides permissions to use the API, but it does not enable the API itself. API enablement is a project-level setting, separate from service account permissions.