<%= form_tag(subscription_path, class: 'newsletter', remote: true) do %>
  <h3 class="newsletter__heading"><%= t('newsletter.heading') %></h3>
  <ul class="list-benefits list-benefits--sm">
    <% t('newsletter.benefits').each do |benefit| %>
      <li><%= benefit %></li>
    <% end %>
  </ul>
  <%= label_tag('subscription[email]', 'Email', class: 'visually-hidden') %>
  <div class="newsletter__form-controls js-newsletter-form">
    <p class="newsletter__error js-newsletter-error-msg">Please provide a valid email</p>
    <%= email_field_tag('subscription[email]', nil, class: 'newsletter__input') %>
    <%= button_tag('Sign up', type: 'submit', class: 'button button--input newsletter__button') %>
  </div>
<% end %>

<%= form_tag(subscription_path, class: 'newsletter', remote: true) do %>
  <%= hidden_field_tag :authenticity_token, form_authenticity_token -%>
  <h3 class="newsletter__heading"><%= t('newsletter.heading') %></h3>
  <ul class="list-benefits list-benefits--sm">
    <% t('newsletter.benefits').each do |benefit| %>
      <li><%= benefit %></li>
    <% end %>
  </ul>
  <%= label_tag('subscription[email]', 'Email', class: 'visually-hidden') %>
  <div class="newsletter__form-controls js-newsletter-form">
    <p class="newsletter__error js-newsletter-error-msg">Please provide a valid email</p>
    <%= email_field_tag('subscription[email]', nil, class: 'newsletter__input') %>
    <%= button_tag('Sign up', type: 'submit', class: 'button button--input newsletter__button') %>
  </div>
<% end %>

Add authenticity token to newsletter sign up form.
Add authenticity token to newsletter sign up form.
