Error: HTTP Error: 400, Cloud Run service X does not exist in region Y in this project.

I have seen two people report this and both resolved because of a region being down temporarily or a small typo. I don't think these apply for me. I believe the service does exist in the specified region. Any ideas what else would cause this error?

Firebase hosting is being used to allow a custom domain as access to the host and the Cloud Run service. If I use the Cloud Run run.app URL for the service, it works as expected. The error is displayed in CLI after command "firebase deploy". The firebase.json file has the rewrites shown below to allow linking firebase host to Cloud Run service. If I don't include the rewrites below, the host (custom domain) URL works fine, of course with exception that it does not link to the Cloud Run service.

"rewrites": [
      {
        "source": "/uxb-bldr",
        "run":
  {
    "serviceId": "mbird-bldr-no-atlas",
    "region": "us-central1"
  }
      },
      {
        "source": "**",
        "destination": "/index.html"
      }
    ]

I did not use the Integration method of linking a Firebase host to an existing Cloud Run service. I developed the Cloud Run service. I developed the firebase host. Then I followed instructions at (https://firebase.google.com/docs/hosting/full-config#rewrite-cloud-run-container) to link the two.