title: Mailchimp API 2.0 lists/subscribe responding with error 250 List_MergeFieldRequired MMERGE4 is required
body: <p>I'm attempting to use the <a href="https://apidocs.mailchimp.com/api/2.0/lists/subscribe.php" rel="nofollow">lists/subscribe</a> Mailchimp API 2.0 endpoint to subscribe an email to a list, but I keep getting a puzzling error.  My request looks like:</p>
  
  <pre><code>{
      "apikey":"myapikey-us5",
      "id":"listid",
      "email":{"email":"my@email.com"},
      "double_optin":false,
      "send_welcome":true
  }
  </code></pre>
  
  <p>I'm sending this to <code>https://us5.api.mailchimp.com/2.0/lists/subscribe.json</code> and getting this response:</p>
  
  <pre><code>{
      "status": "error",
      "code": 250,
      "name": "List_MergeFieldRequired",
      "error": "MMERGE4 must be provided - Please enter a value"
  }
  </code></pre>
  
  <p>And if I specify <code>"merge_vars": {}</code> I still get the same error.  What am I missing here?  </p>