How to bind one input for two params' values?

I have a problem with my nested form Here is it:

  <%= form_for :project, method: :patch do |f| %>

  <%= f.fields_for :todos_attributes do |todo_form| %>

      <p>
        <%= todo_form.text_field :text, placeholder:"Task name..."%>
      </p>

      <p>
        <%= todo_form.collection_select(:project_id, @projects, :id, :title) %>
      </p>
  <% end %>

  <a href="javascript:undefined" class="hideDiv">Cancel</a>
  <%= f.submit %>
<% end %>

Here is my ProjectsController code to update selected project:

  def update

    @project = Project.find(params[:id])
    @project.update(todo_params)

    redirect_to root_path
  end

  def todo_params
    params.require(:project).permit(:id, todos_attributes: [:text, :project_id])
  end

The problem is that I get an error in update method: "Couldn't find Project with 'id'=index" "index" as understand is default value. How can I set it to be equal to the value(:project_id) selected in collection_select in the form? Thank you!