TWIML with url attribute on Number not called

so I create an outbound call with makeCall which allows you to specify a url that that twilio will use when placing the call. That part works, twilio uses the URL specified in makeCall and calls my server. Now, I respond with a TWIML as shown below.

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <Dial>
    <Number url="SOME_VALID_URL" method="POST">
      SOME_E_164_NUMBER
    </Number>
  </Dial>
</Response>

According to the Twilio documentation for Number, this should work. My test server never sees the call from Twilio specified by the url param in Number.

I am using ngrok to talk to my local server and it does work. That is not the problem. So, what am I doing wrong?

via Vincent Agnello