Server error: `POST https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/ublog-prod-secret-accessor-sa@hket-ul-ublog-prod.iam.gserviceaccount.com:generateAccessToken` resulted in a `503 Service Unavailable` response:
{
  "error": {
    "code": 503,
    "message": "The service is currently unavailable.",
    "status": "UNAVAILABLE"
  }
 (truncated...)