go-org | Org mode parser with html | Static Site Generator library

I am trying to update an existing Django app's login process because of a problem I have with the invitation links. If I send an invitation link it works as expected and takes the user through the sign-up form and into the site, but if they try to use that invitation link later to access the site again it give a 500 error (DoesNotExist: User matching query does not exist.). I want to redirect all expired invitation links to the main login page so that they can just login rather than going to the 500 error page.

I am using Django 1.11 and the invitation backend (http://django-organizations.readthedocs.io/en/latest/reference/backends.html)

I see that it has a get_success_url that I can use to send the original login to a home page, but is there a get_fail_url that I can use to send expired invitation links to a main login page? Or is there a better way to approach this problem?

Here is my CustomerInvitations class that I send all /invitation/ urls to: