Background Recently, the LINE business card assistant robot ( linebot-namecard-python ) deployed on Google Cloud Run suddenly went down. After checking the logs with gcloud logging read , the following ruthless error appeared: google.api_core.exceptions.ResourceExhausted: 429 Your billing account has exceeded its monthly spending cap. It turned out that we used the API Key provided by Google AI Studio ( google.generativeai package) for rapid development, and as a result, we silently maxed out the monthly free quota. As a developer who needs to launch a service, it's time to "level up" the architecture and migrate the model calls to the enterprise-grade Google Cloud Vertex AI , directly using GCP's IAM permissions and billing system. This article will share the migration process and the various pitfalls encountered along the way.…