title: Using update_user_meta to update taxonomy checkbox field
body: <p>I have an ACF taxonomy field for my WordPress users which is set as a 'checkbox' type. This contains a list of 'keywords'. I then have a sign up form on the website which allows users to choose their 'keywords'. When they submit that form, a WordPress user account is created for them and I then need to programatically update their ACF keywords list based on the keywords they have selected.</p>
  
  <p>I have tried to do this using the 'update_user_meta' function but that doesn't seem to work. Has anyone managed to work out how to do this?</p>
  
  <p>Below is an example of how I tried using 'update_user_meta':</p>
  
  <pre><code>if(isset($_POST['keywords'])) {
      foreach($_POST['keywords'] as $keyword) {
          update_user_meta(1, 'keywords', $keyword);
      }
  }
  </code></pre>
  
  <p>^ where $_POST['keywords'] contains an array of keywords that the user has selected</p>