title: firebase/firestore get nested collection
body: <p>I have a document that has a nested collection. I've been trying to get that nested collection using <code>the firebase/firestore</code> library as documented here:  <a href="https://firebase.google.com/docs/reference/js/firebase.firestore" rel="noreferrer">https://firebase.google.com/docs/reference/js/firebase.firestore</a></p>
  
  <pre><code>let route = await firebase.firestore()
  .collection('route')
  .doc('0bayKbCiAchc0Vy9XuxT')
  .collection('qa')
  .get()
  </code></pre>
  
  <p>I just get back <code>PayloadTooLargeError: request entity too large</code></p>
  
  <p>Any ideas? Is this not supported with this library?</p>