How do I fix 503: Service Unavailable for Billing Transaction Error
<p>I'm getting a 503 error regarding billing when trying to start a survey I've created via the API (POST <a href="https://www.googleapis.com/consumersurveys/v2/surveys" rel="nofollow">https://www.googleapis.com/consumersurveys/v2/surveys</a>). Is this something I can fix or does GCS need to make backend billing changes?</p>

<p><strong>Request</strong></p>

<pre><code>POST /consumersurveys/v2/surveys/pbn22yzmfnvaqwsiz2k5jbgx3i/start
</code></pre>

<p><strong>Response</strong></p>

<pre><code>HTTP/1.1 503 Service Unavailable
Content-length: 732
X-xss-protection: 1; mode=block
X-content-type-options: nosniff
Expires: Tue, 24 May 2016 20:56:17 GMT
Vary: Origin,X-Origin
Server: GSE
Cache-control: private, max-age=0
Date: Tue, 24 May 2016 20:56:17 GMT
X-frame-options: SAMEORIGIN
Content-type: application/json; charset=UTF-8
{
  "error": {
    "code": 503, 
    "message": "Billing Transaction Error: Account must be a service account with billing enabled to start/stop a survey. Use 2-Legged OAuth and contact 'gcs-api@google.com' to enable billing.. Request Id: 5744bff000ff04244be71b067a0001737e3430322d747269616c320001707573682d30352d32342d72303400010111", 
    "errors": [
      {
        "domain": "global", 
        "message": "Billing Transaction Error: Account must be a service account with billing enabled to start/stop a survey. Use 2-Legged OAuth and contact 'gcs-api@google.com' to enable billing.. Request Id: 5744bff000ff04244be71b067a0001737e3430322d747269616c320001707573682d30352d32342d72303400010111", 
        "reason": "BILLING_TRANSACTION_ERROR"
      }
    ]
  }
}
</code></pre>