title: Request to Google Endpoints Quickstart API Fails with a 503
body: <p>I am working through the Quickstart for Cloud Endpoints Frameworks on Google App Engine. After deploying the app I try to send a request to the API as outlined in the Quickstart: </p>
  
  <pre><code>curl -H "Content-Type: application/json" -X POST -d '{"content":"Hello world!"}' https://[my-app].appspot.com/_ah/api/echo/v1/echo
  </code></pre>
  
  <p>It returns the following error message:</p>
  
  <pre><code>{
   "error": {
    "code": 503,
    "errors": [
     {
      "domain": "global",
      "message": "Internal Server Error",
      "reason": "backendError"
     }
    ],
    "message": "Internal Server Error"
   }
  }
  </code></pre>
  
  <p>There are 4 APIs created in the endpoints-frameworks-v2/echo sample. I get the same error message when I go to the API explorer and try to test the first 3 APIs. The last API get_user_email works as expected after after I authorise and execute it. </p>
  
  <p>Any help would be great.</p>