account.rb

class Account < ApplicationRecord
  
  # ......

  validates :name, presence: true, uniqueness: { case_sensitive: false }	  validates :name, presence: true, uniqueness: { case_sensitive: false }


  def create(user:)
    account_groups.create(user: user)
    account_owners.create(user: user)
  end
  
  # .....
end

new.html.erb

<%= render 'devise/shared/form_shell', captured: capture { %>
  <%= simple_form_for(resource, as: resource_name, url: registration_path(resource_name), wrapper: :vertical_form) do |f| %>
      <%= f.input :email, autocomplete: "email", required: true, autofocus: true %>

      <%= f.input :account_name, label: 'Account Name', placeholder: 'Name of your organization' %>

      <div class="mt-6">
        <%= f.input :password, autocomplete: "new-password" %>
        <% if @minimum_password_length %>
        <em>(<%= @minimum_password_length %> characters minimum)</em>
        <% end %><br />
      </div>

      <div class="mt-6">
        <span class="block w-full rounded-md shadow-sm">
          <%= f.submit "Sign up", class: tw_full_width_button %>
          <%= recaptcha_execute('signup') if Rails.env.production? %>
        </span>
      </div>
    <% end %>
<% } # capture %>

registrations_controller.rb

class Users::RegistrationsController < DeviseInvitable::RegistrationsController
  before_action :configure_sign_up_params, only: [:create, :update]

  def update
    user = build_resource(sign_up_params)
    if user.valid?
      super
    else
      render 'edit'
    end
  end

  def create
    render 'new' and return if sign_up_captcha_failed?
    user, account = prepare_resources
    if user.valid? && account.valid?
      account.save!
      super do |res|
        account.create(user: res)
      end
      first_time_user! if resource.persisted?
    else
      user.errors.add(:account_name, account.errors[:name].join(',')) unless account.valid?
      resource.account_name = params[:user][:account_name]
      render 'new'
    end
  end

  ## ....

  protected

  def configure_sign_up_params
    devise_parameter_sanitizer.permit(:sign_up, keys: [:account_name])
  end 

  ## .....
end

simple_form_tailwind.rb

# Use this setup block to configure all options available in SimpleForm.
require_relative '../../app/helpers/tailwind_helper'

SimpleForm.setup do |config|
	config.error_notification_class = 'alert alert-danger'
	config.button_class = 'btn btn-default'
	config.boolean_label_class = nil
  include TailwindHelper

	config.wrappers :vertical_form, tag: 'div', class: "mt-6", error_class: 'border-red-400 border-dashed' do |b|
		b.use :html5
		b.use :placeholder
		b.optional :maxlength
		b.optional :pattern
		b.optional :min_max
		b.optional :readonly
    b.use :label, class: tw_label
    b.wrapper tag: 'div', class: "mt-1 rounded-md shadow-sm" do |i|
      i.use :input, class: tw_field
      i.use :error, wrap_with: { tag: 'span', class: 'p-1 bg-red-200' }
      i.use :hint,  wrap_with: { tag: 'p', class: 'p-1 bg-orange-400' }
    end
	end
end

user.rb

class User < ApplicationRecord
  # .....
  
  attribute :account_name, :string # only used for the sign up form
  
  # ....
end