[Answered ]-Django {% url %} template looping

You should write a space between the == and the "staff" string, so:

{% if request.session.sub == "staff" %}
    …
{% endif %}

as for the URL, you not refer to a URL which is an include(…) since that is a collection of URLs. For example:

<a href="{% url 'staff:customers' link.linkfield as the_url %}" class="nav-link">