I have installed django-comments-xtd following the quick start guide in the documentation here.
When I go to access the /comments URL, I only get a 404 error, and the message 'Raised by: wagtail.wagtailcore.views.serve'.
I followed the documentation without issue, and have installed other apps that work fine such as django-machina.
I am using django 1.11.13, python 2.7 and django-comments-xtd 2.1.0.
Why would this particular URL not be accessible? Templates exist in the correct location.
My files are setup exactly the same as in the documentation, happy to provide more info but not sure what to provide right now.
What can I do to try and troubleshoot the problem?
I think you are misreading the documentation and you do not actually have a problem. It just says:
mount the URL patterns of django_comments_xtd in the path /comments/
It does not say that you should access this URL. The fact that, as per your comment, you are not getting a 404 when you are accessing /comments/sent/ indicates that you have set up django-comments-xtd correctly.
For /comments/ to be a valid URL, the django_comments_xtd.urls you included would have to contain an empty URL pattern, like this:
url('', some_view)
If you look at the urls.py of django-comments-xtd, you will see that it does indeed include the urls.py from django-contrib-comments, but this doesn't define an empty URL pattern. So there is no URL pattern that would match /comments/.