title: 400 Bad Request When Adding Member to MailChimp List
body: <p>I am sending a <code>POST</code> request to <a href="http://developer.mailchimp.com/documentation/mailchimp/reference/lists/members/" rel="nofollow noreferrer">the following resource</a> and getting a 400. I understand <a href="http://developer.mailchimp.com/documentation/mailchimp/guides/error-glossary/" rel="nofollow noreferrer">what the error means</a>, but still am unsure why I'm getting it when a <code>GET</code> request to the same resource works.</p>
  
  <pre><code>/lists/{list_id}/members
  </code></pre>
  
  <p>Here is a exerpt of the code:</p>
  
  <pre><code>$client = new \GuzzleHttp\Client();
  
  $response = $client-&gt;request('POST', // &lt;-- Drop in a GET here and it works, other than it's not the behavior I need.
      env('MAILCHIMP_API_URL') . 'lists/' . env('MAILCHIMP_LIST_KEY') . '/members',
      [
          'auth'  =&gt; ['app', env('MAILCHIMP_API_KEY')],
          'query' =&gt; [
              'email_address' =&gt; 'donnie@test.com',
              'email_type'    =&gt; 'html',
              'status'        =&gt; 'subscribed',
          ]
      ]);
  
  dd($response-&gt;getStatusCode());
  </code></pre>
  
  <p>Response</p>
  
  <pre><code>Client error: `POST https://XXXX.api.mailchimp.com/3.0/lists/XXXX/members?email_address=donnie%40test.com&amp;email_type=html&amp;status=subscribed`
  resulted in a `400 Bad Request`
  response: {
    "type": "http://developer.mailchimp.com/documentation/mailchimp/guides/error-glossary/",
    "title": "Invalid Resource",
    "status": 400,
    "detail": "The resource submitted could not be validated. For field-specific details, see the 'errors' array.",
    "instance": "f32e7076-b970-4f5c-82c6-eec5875e83b4",
    "errors": [{
      "field": "",
      "message": "Schema describes object, NULL found instead"
    }]
  }
  </code></pre>