Add additional details to staff order notification

[Valee]

I added some custom fields at the cart page, which are added to an order as additional details. I would like to add these to the Staff Order Confirmation and to the Fullfilment service notification. I tried  to add several codes, but it doesn't work. Example: 

<tr>
<td>
<strong>Uitsparing</strong><br/>
<p>
<ul> {% for attribute in order.attributes -%}
<li><strong>{{ attribute.first }}:</strong> {{ attribute.last }}</li>
{%- endfor %}
</ul></p>
</td>
</tr>

What am I doing wrong? How can I add this?