Rails simple-form association not saving - ruby-on-rails

Question

Am new to RoR and Simple_form. I have a simple set-up where I have an association between 2 classes. The form I use is not updating/saving and always setting the value back to blank. Looked at the docs and other postings, what am I doing wrong?
Classes
class Annotation < ApplicationRecord
has_many :comments, dependent: :destroy
belongs_to :documenttype
has_attached_file :file, styles: { large: "600x600>", medium: "500x500>", thumb: "150x150#" }, default_url: "/images/:style/missing.png"
accepts_nested_attributes_for :documenttype
validates_attachment_content_type :file, content_type: ['image/jpeg', 'image/png', 'image/gif', 'application/pdf']
validates :name, presence: true, uniqueness: true, length: { minimum: 10, maximum: 50 }
validates :description, length: { minimum: 20, maximum: 500 }
validates :documenttype, presence: true
validates :file, presence: true
end
class Documenttype < ApplicationRecord
has_many :annotations
validates :name, presence: true, uniqueness: true, length: { minimum: 5 }
end
Params
def annotation_params
params.require(:annotation).permit(:name, :description, :file, :active, :documenttype)
end
def documenttype_params
params.require(:documenttype).permit(:name, :description, :active, annotation_attributes: [:id, :name])
end
This is the form...
<div class="container-fluid">
<div class="row">
<div class="col-md-6">
<%= simple_form_for #annotation, html: { class: 'form-horizontal', multipart: true },
wrapper: :horizontal_form,
wrapper_mappings: {
check_boxes: :horizontal_radio_and_checkboxes,
radio_buttons: :horizontal_radio_and_checkboxes,
file: :horizontal_file_input,
boolean: :horizontal_boolean
} do |f| %>
<%= f.error_notification %>
<%= f.input :name, placeholder: 'Enter name' %>
<%= f.input :description, placeholder: 'Description' %>
<%= f.association :documenttype %>
<%= f.input :active, as: :boolean %>
<% if #annotation.file.blank? %>
<%= f.input :file, as: :file %>
<% else %>
<% end %>
<%= f.button :submit %>
<% unless #annotation.file.blank? %>
<%= link_to ' Annotate', annotations_path, :class => "btn btn-default" %>
<% end -%>
<% end %>
<p><br><%= link_to 'List' , annotations_path %></p>
</div>
<div class="col-md-6">
<% unless #annotation.file.blank? %>
<%= image_tag #annotation.file.url(:large) %>
<% end %>
</div>
</div>

Answer 1

I found the solution; I needed to add :documenttype_id to annotation_params.