Problems getting routes to work

I am creating a form_for , and am getting this error:

function UrmedWebappWeb.Router.Helpers.diagnosis_symptom_path/3 is undefined or private

In my router, I have:

resources "/diagnosis_symptom", DiagnosisSymptomController

my routes shows:

diagnosis_symptom_path  PATCH   /diagnosis_symptom/:id                      UrmedWebappWeb.DiagnosisSymptomController :update

My form render looks like:

<%= render(UrmedWebappWeb.DiagnosisSymptomView,
    "form.html", Map.put(assigns, :action, Routes.diagnosis_symptom_path(@conn, :update, ds))) %>

I am making a very similar call somewhere else on this, and it works. If I replace my routes pathname with the one for the other path that works, this works in place.

I am sure I just forgot something somewhere. Does anyone see my goof?