flask_flashed_messages.html

{% with messages = get_flashed_messages(category_filter=["error"]) %}
{% if messages %}
<div class="panel panel-danger">
  <div class="panel-heading">
    Error
  </div>
  <div class="panel-body">
    <ul class=flashes>
    {% for message in messages %}
      <li>{{ message }}</li>
    {% endfor %}
    </ul>
  </div>
</div>
{% endif %}
{% endwith %}