How do I show errors from related tables on form creation attempts

I am able to somewhat accomplish what I am looking for, but not exactly. Saving the form when the defualt "Select a subscription" text is selected never turns out correctly. I have a form that pulls in a select from a related database:

<%= form_for [current_user, @subscription] do |f| %>
  <% if @subscription.errors.any? %>
    <div class="error_messages">
      <h2>Form is invalid</h2>
      <ul>
        <% for message in @subscription.errors.full_messages %>
          <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>
  <p>
    <%= f.label :subscription_types, "Subscription Type" %><br />
    <%= f.collection_select :subscription_type_id, @subscription_types, :id, :type_name, :prompt => "Select a subscription" %>
  </p>
  <p class="button"><%= f.submit %></p>
<% end %>

And I have a model that validates the the related id

class Subscription < ActiveRecord::Base
    belongs_to :subscription
    belongs_to :subscription_type

validates_presence_of :subscription_type_id, :on => :create, :message => "You need to select a subscription type"
end

When I try and save the form and the create action is called, the current code returns a nested array printed out to the screen. Originally, I had the "redirect_to" method set to new, but I don't think it was running the new action and establishing the variables. I set to to redirect_to in order to go through the action details, but now the errors do not set correctly. I feel that I could probably get what I need with enough tinkering, but is there a good way to pull these messages out?

class SubscriptionsController < ApplicationController
    def new
        puts "FAAAAAAAAAAAART-2"
        @subscription = Subscription.new
        @subscription_types = SubscriptionType.all
        puts @subscription_types 
        puts "FAAAAAAAAAAAART-3"
    end

    def create
        @subscription = Subscription.new(subscription_params)
        @user = User.find(session[:user_id])
        @subscription.user_id = @user.id
        if @subscription.save
            redirect_to root_url, :notice => "Subscription Created!"
        else
            puts "FAAAAAAAAAAAART-1"
            flash[:error] = @subscription.errors.messages.values()
            redirect_to action: :new
        end
    end

    private

    def subscription_params
        params.require(:subscription).permit(:subscription_type_id)
    end
end