title: Add users to interest group via MailChimp API v2.0
body: <p>I want to add a subscriber to an interest group via the MailChimp API.</p>
  
  <p>This is my <code>$merge_vars</code> array:</p>
  
  <pre><code>$merge_vars = array(
      'GROUPINGS' =&gt; array(
          0 =&gt; array(
              'id' =&gt; 17385, // The group list ID
              'groups' =&gt; "Test 123", // A test group, that does exist
          )
      )
  );              
  </code></pre>
  
  <p>and this is how I'm updating the member:</p>
  
  <pre><code>$update = $mc-&gt;lists-&gt;updateMember(self::$mainListID, $email, $merge_vars);
  </code></pre>
  
  <p>Here's a <code>var_dump($merge_vars)</code>:</p>
  
  <pre><code>array(1) {
    ["GROUPINGS"]=&gt;
    array(1) {
      [0]=&gt;
      array(2) {
        ["id"]=&gt;
        int(17385)
        ["groups"]=&gt;
        string(8) "Test 123"
      }
    }
  }
  </code></pre>
  
  <p>and <code>$email</code> is a struct, here's <code>$var_dump($email)</code>:</p>
  
  <pre><code>array(1) {
    ["email"]=&gt;
    string(11) "my@mail.com"
  }
  </code></pre>
  
  <p>I'm about to be driven to distraction, because the API doesn't return an error, everything seems to go smoothly, except for the big problem of the user not being added to the list.</p>
  
  <p>I've looked at <a href="https://stackoverflow.com/questions/8761595/mailchimp-api-php-add-to-interest-group/8809708#8809708" title="this question">this question</a> which helped me get so far, but the version of the API it uses is 1.3 and that might have something to do with it.</p>
  
  <p>What am I doing wrong?</p>