Cannot get a nested model to save in rails 5 - ruby-on-rails

Question

I have a user which is a nested resource of account, and I'm trying to create the account and the user in 1 form. The account is saving correctly, however no user record is being written.
user.rb:
class User < ApplicationRecord
belongs_to :account
validates :email, presence: true
end
account.rb:
class Account < ApplicationRecord
has_many :users, :dependent => :destroy
accepts_nested_attributes_for :users
end
accounts_controller.rb:
class AccountsController < ApplicationController
def new
#account = Account.new
#user = #account.users.build
end
def create
#account = Account.new(account_params)
#account.secret = SecureRandom.uuid
if #account.save
flash[:success] = "You've successfully created your account, now it's time to create your first team."
redirect_to dashboard_path
else
flash[:danger] = "There was a problem creating your account"
redirect_to signup_path
end
end
private
def account_params
params.require(:account).permit(:name, user_attributes: [:first_name, :last_name, :email, :password, :password_confirmation, :secret])
end
end
accounts/new.html.erb:
<h1>Signup</h1>
<div class="row">
<div class="col-md-6 col-md-offset-3">
<%= form_for(#account) do |form| %>
<%= form.label "Account name" %>
<%= form.text_field :name, class: "form-control" %>
<%= form.fields_for :user do | f| %>
<%= f.label :first_name %>
<%= f.text_field :first_name, class: "form-control" %>
<%= f.label :last_name %>
<%= f.text_field :last_name, class: "form-control" %>
<%= f.label :email %>
<%= f.text_field :email, class: "form-control" %>
<%= f.label :password %>
<%= f.password_field :password, class: "form-control" %>
<%= f.label :password_confirmation, "Confirmation" %>
<%= f.password_field :password_confirmation, class: "form-control" %>
<% end %>
<%= form.submit "Signup", class: "btn btn-primary" %>
<% end %>
</div>
</div>
When I submit the the form and check my logs, I'm seeing:
Processing by AccountsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"p5+CRICRp3ZilIg1NtehEQG7Gh2amnFFUD5NawtqkICJ4uRDvvJxf2WTbd7+rnfG9zdblT1QWgfJ62NNxcc2RA==", "account"=>{"name"=>"Streame", "user"=>{"first_name"=>"Jeremy", "last_name"=>"Kirkham", "email"=>"jeremy#streame.com.au", "password"=>"[FILTERED]", "password_confirmation"=>"[FILTERED]"}}, "commit"=>"Signup"}
Unpermitted parameter: user

Answer 1

The answer was quite simple in the end - I needed to change the form from
<%= form.fields_for :user do | f| %>
to
<%= form.fields_for :users do | f| %>
(note user -> users), and the controller from
params.require(:account).permit(:name, user_attributes:
to
params.require(:account).permit(:name, users_attributes:
(again note user -> users).
Basically it came down to pluralisation!