1👍
You can only put i if you put int value. If you want to call a string you must put the variable with the value like this.
<p>{% for i in l %}
Sample 1: <a href="{% url produit_detail letter=i %}">{{ i }}</a>
Sample 2: <a href="{% url appli:produit_detail letter=i %}">{{ i }}</a>
Sample 3: <a href="/manager/produit/detail/{{i}}">{{ i }}</a>
{% endfor %}
</p>You did not put value for letter
Source:stackexchange.com