Undefined Method Error - Single Table Inheritance - Routing error

Question

I am creating a Single Table Inheritance model to build a comment thread and I am getting a confusing routing error

I have set up my Model

class Question < ApplicationRecord
  has_many :answers, class_name: 'Questions::Answer'
end

class Answer < ApplicationRecord
  has_many :answers, class_name: 'Answers::Answer'
end

with associated sub classes

module Questions
  class Answer < ::Answer
    belongs_to :question
    validates :body, presence: true
    validates :question, presence: true
  end
end

module Answers
  class Answer < ::Answer
    belongs_to :answer
    has_one :question, through: :answer
    validates :body, presence: true
    validates :answer, presence: true
  end
end

Routes

resources :questions do 
    resources :answers, shallow: true 
end

In my view, I render answers and a form to add an answer

<%= render @answers %></br>
<%= render "answers/form" %>

Which takes the following instances from my Question controller

 def show
    @answer = @question.answers.new
    @answers = @question.answers.page(params[:page]).per(5)
 end

However, this gives me an undefined method error: undefined method `questions_answers_path'

In my routes, indeed the only paths are

question_answers     GET    /questions/:question_id/answers(.:format)       answers#index
                     POST   /questions/:question_id/answers(.:format)       answers#create
new_question_answer  GET    /questions/:question_id/answers/new(.:format)   answers#new
edit_answer          GET    /answers/:id/edit(.:format)                     answers#edit
answer               GET    /answers/:id(.:format)                          answers#show         
                     PATCH  /answers/:id(.:format)                          answers#update       
                     PUT    /answers/:id(.:format)                          answers#update       
                     DELETE /answers/:id(.:format)                          answers#destroy

The question then is, why is it looking for the plural questions_answers_path, rather than question_answers_path.

The form is relatively standard:

<%= simple_form_for(@answer) do |f| %>
  <%= f.error_notification %>
  <%= f.error_notification message: f.object.errors[:base].to_sentence if f.object.errors[:base].present? %>

  <div class="form-inputs">
  <%= f.input :body %>
  </div>

  <div class="form-actions">
    <%= f.button :submit %>
  </div>
<% end %>

When I force the path by using <%= simple_form_for @answer, url: question_answers_path(@question) do |f| %> I get an error trying to submit the form. Body can't be blank

Any ideas on what is wrong with my code?

For completeness: Answers Controller

class AnswersController < ApplicationController
  before_action :set_answer, only: [:edit, :update, :destroy]
  before_action :set_question

  def create
    @answer = @question.answers.build(answer_params)

    respond_to do |format|
      if @answer.save
        format.html { redirect_to question_path(@question) }
        format.json { render :show, status: :created, location: @answer }
      else
        format.html { render :new }
        format.json { render json: @answer.errors, status: :unprocessable_entity }
      end
    end
  end

  def update
    authorize @answer
    respond_to do |format|
      if @answer.update(answer_params)
        format.html { redirect_to question_answers_path(@question), notice: 'Answer was successfully updated.' }
        format.json { render :show, status: :ok, location: @answer }
      else
        format.html { render :edit }
        format.json { render json: @answer.errors, status: :unprocessable_entity }
      end
    end
  end

  def destroy
    authorize @answer
    @answer = Answers.find(params[:id])
    @answer.discard
    respond_to do |format|
      format.html { redirect_to question_answers_path(@question), notice: 'Answer was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    def set_answer
      @answer = Answer.find(params[:id])
    end

    def answer_params
      params.fetch(:answer, {}).permit(:body, :type).merge(user_id: current_user.id, question_id: @question.id)
    end

    def set_question
      @question = Question.find(params[:question_id])
    end

end