title: Firebase Rest API status code 18
body: <p>I'm performing a multi-path update to Firebase that results in receiving the <a href="https://www.firebase.com/docs/rest/api/#section-error-conditions" rel="nofollow noreferrer"><em>undocumented</em> error code 18</a>.</p>
  
  <p>I can perform the multi-path update in smaller chunks, and I receive a successful 200, but when it is all in one, the request fails. Also, I know the request is formed correctly as I've made sure to beware <a href="https://stackoverflow.com/questions/36624969/firebase-multi-path-update-invalid-data-couldnt-parse-json-object-array-or">the multi-path update pitfall explained here</a>.</p>
  
  <p>So, what's the deal?</p>