Couldn't find User without an ID when calling method - ruby-on-rails

Question

I got a modal, with a form inside it. However I get the classic error when I try to submit:
Couldn't find User without an ID
My form looks like this:
<%= form_for add_email_users_path, url: { action: 'add_email', controller: 'users' } do |f| %>
<%= f.email_field :email, placeholder: 'Your email address', class: 'input-lg form-control' %>
<%= f.button 'Continue', class: 'btn btn-success', 'data-disable-with' => "Saving <i class='fa fa-spinner fa-spin'></i>".html_safe %>
<% end %>
routes:
resources :users, except: [:destroy] do
post 'add_email', on: :collection
end
User_controller:
def add_email
#user = User.find(params[:id])
if #user.update_attributes(setup_params)
redirect_to campaigns_path, notice: 'Thank you for adding your email!'
else
redirect_to :back, alert: 'Unable to save your email'
end
end

Answer 1

Try this:
<%= form_for add_email_users_path(#user) do |f| %>
<%= f.email_field :email, placeholder: 'Your email address', class: 'input-lg form-control' %>
<%= f.button 'Continue', class: 'btn btn-success', 'data-disable-with' => "Saving <i class='fa fa-spinner fa-spin'></i>".html_safe %>
<% end %>
and your route:
resources :users, except: [:destroy] do
post 'add_email', on: :member
end

Answer 2

You have the wrong path method in your form_for, it should be:
add_email_user_path(#user)
And your route should be for member not collection:
post 'add_email', on: :member
Here is what your stuff should look like:
form.html.erb
<%= form_for add_email_user_path(#user) do |f| %>
<%= f.email_field :email, placeholder: 'Your email address', class: 'input-lg form-control' %>
<%= f.button 'Continue', class: 'btn btn-success', 'data-disable-with' => "Saving <i class='fa fa-spinner fa-spin'></i>".html_safe %>
<% end %>
routes.rb
resources :users, except: [:destroy] do
post :add_email, on: :member
end
Take special note of the change to the form_for call.

Answer 3

It can't be a collection method as it is looking for specific id define it as a member method
resources :users, except: [:destroy] do
member do
post :add_email
end
end
In form
<%= form_for add_email_user_path(#user), method: :post do |f| %>
You can refer to this docs to understand member and collection methods