Rails 4 simple_form has_many through check boxes not saving

<div id="client_approved_buttons" class="btn-group" data-toggle="buttons-radio">
  <%= f.input : client_approved, as: :hidden %>
  <a class="btn" data-value="1">Yes</a>
  <a class="btn" data-value="0">No</a>
</div>

// make button toggles update hidden field
$('.btn-group a').on('click', function(event){
  event.preventDefault();
  var input = $(this).siblings('.control-group').find('input[type=hidden]');
  if(input.length>0){
    if(input.val().toString() !== $(this).data('value').toString()){
      input.val($(this).data('value')).trigger('change');
    }
  }
});

  def configure_permitted_parameters
    devise_parameter_sanitizer.for(:sign_up) { |u| u.permit(:username, :email, :password, :position_ids => []) }
  end

def comment_params
  params.require(:comment).permit(:post_id, :title, :event_ids => [])
end

class UsersController < ApplicationController
  def new
    @user = User.new
    @user.applications.build
  end
end

<%= f.simple_fields_for :applications do |a| %>
  <%= a.input :over_18, label: 'Are you over 18?', as: :radio_buttons %>
<% end %>