title: Why "Invalid Content Type"
body: <p>Trying to update a data field on a lead record in Marketo.  Using <strong>C#</strong>.  I send:</p>
  
  <pre><code>{"action":"updateOnly","input":[{"email":"dfranks@gmail.com","leadQuality":"Hot"}]}
  </code></pre>
  
  <p>And get back:</p>
  
  <pre><code>{"requestId":"d98e#14b2d7dd1f3","success":false,"errors":[{"code":"612","message":"Invalid Content Type"}]}
  </code></pre>
  
  <p>Why the Invalid Content type message?  The field <code>leadQuality</code> is legit.  The email address exists.  I've tried a number of different fields and always the same message.  Access token is good too.</p>