pubsubTopic

Optional. The name of the Pub/Sub topic where budget related messages will be published, in the form projects/{project_id}/topics/{topic_id}. Updates are sent at regular intervals to the topic. The topic needs to be created before the budget is created; see https://cloud.google.com/billing/docs/how-to/budgets-programmatic-notifications for more details. Caller is expected to have pubsub.topics.setIamPolicy permission on the topic when it's set for a budget, otherwise, the API call will fail with PERMISSION_DENIED. See https://cloud.google.com/billing/docs/how-to/budgets-programmatic-notifications#permissions_required_for_this_task for more details on Pub/Sub roles and permissions.