Can't display dashboard widget content

I’m trying to display dashboard widget content and i get the message

Warning: call_user_func() expects parameter 1 to be a valid callback, function ‘couponsgen_create_dashboard_widget’ not found or invalid function name in C:\wamp\www\wpdev1\wp-admin\includes\template.php on line 1037

My code for creating the widget is

<?php

class Couponsgen_Admin {

	/**
	 * The ID of this plugin.
	 *
	 * @since    1.0.0
	 * @access   private
	 * @var      string    $plugin_name    The ID of this plugin.
	 */
	private $plugin_name;

	/**
	 * The version of this plugin.
	 *
	 * @since    1.0.0
	 * @access   private
	 * @var      string    $version    The current version of this plugin.
	 */
	private $version;

	/**
	 * Initialize the class and set its properties.
	 *
	 * @since    1.0.0
	 * @param      string    $plugin_name       The name of this plugin.
	 * @param      string    $version    The version of this plugin.
	 */
	public function __construct( $plugin_name, $version ) {

		$this->plugin_name = $plugin_name;
		$this->version = $version;

	}

	/**
	 * Register the stylesheets for the admin area.
	 *
	 * @since    1.0.0
	 */
	public function enqueue_styles() {

		/**
		 * This function is provided for demonstration purposes only.
		 *
		 * An instance of this class should be passed to the run() function
		 * defined in Couponsgen_Loader as all of the hooks are defined
		 * in that particular class.
		 *
		 * The Couponsgen_Loader will then create the relationship
		 * between the defined hooks and the functions defined in this
		 * class.
		 */

		wp_enqueue_style( $this->plugin_name, plugin_dir_url( __FILE__ ) . 'css/couponsgen-admin.css', array(), $this->version, 'all' );

	}

	/**
	 * Register the JavaScript for the admin area.
	 *
	 * @since    1.0.0
	 */
	public function enqueue_scripts() {

		/**
		 * This function is provided for demonstration purposes only.
		 *
		 * An instance of this class should be passed to the run() function
		 * defined in Couponsgen_Loader as all of the hooks are defined
		 * in that particular class.
		 *
		 * The Couponsgen_Loader will then create the relationship
		 * between the defined hooks and the functions defined in this
		 * class.
		 */

		wp_enqueue_script( $this->plugin_name, plugin_dir_url( __FILE__ ) . 'js/couponsgen-admin.js', array( 'jquery' ), $this->version, false );

	}

        // call function to create our dashboard widget
        public function couponsgen_add_dashboard_widget() {
            wp_add_dashboard_widget(
                'couponsgen_dashboard_widget',
                'Coupons Generator Dashboard Widget',
                'couponsgen_create_dashboard_widget'
            );
        }

        // function to display our dashboard widget content
        public function couponsgen_create_dashboard_widget() {
           echo "<p>Hello World! This is my couponsgen Dashboard Widget</p>";
        }

        public function add_plugin_admin_menu() {
            add_options_page( 'Coupons Generator plugin Setup', 'Coupons Gen', 'manage_options', $this->plugin_name, array($this, 'display_plugin_setup_page'));
        }

        public function add_action_links( $links ) {
            $settings_link = array(
                '<a href="' . admin_url( 'options-general.php?page=' . $this->plugin_name ) . '">' . __('Settings', $this->plugin_name) . '</a>',
            );
            return array_merge(  $settings_link, $links );

        }

        public function display_plugin_setup_page() {
            include_once( 'partials/couponsgen-admin-display.php' );
        }

}

and for adding the action

<?php

class Couponsgen {

	/**
	 * The loader that's responsible for maintaining and registering all hooks that power
	 * the plugin.
	 *
	 * @since    1.0.0
	 * @access   protected
	 * @var      Couponsgen_Loader    $loader    Maintains and registers all hooks for the plugin.
	 */
	protected $loader;

	/**
	 * The unique identifier of this plugin.
	 *
	 * @since    1.0.0
	 * @access   protected
	 * @var      string    $plugin_name    The string used to uniquely identify this plugin.
	 */
	protected $plugin_name;

        /**
	 * The current version of the plugin.
	 *
	 * @since    1.0.0
	 * @access   protected
	 * @var      string    $version    The current version of the plugin.
	 */
	protected $version;

	/**
	 * Define the core functionality of the plugin.
	 *
	 * Set the plugin name and the plugin version that can be used throughout the plugin.
	 * Load the dependencies, define the locale, and set the hooks for the admin area and
	 * the public-facing side of the site.
	 *
	 * @since    1.0.0
	 */
	public function __construct() {

		$this->plugin_name = 'couponsgen';
		$this->version = '1.0.0';

		$this->load_dependencies();
		$this->set_locale();
		$this->define_admin_hooks();
		$this->define_public_hooks();

	}

	/**
	 * Load the required dependencies for this plugin.
	 *
	 * Include the following files that make up the plugin:
	 *
	 * - Couponsgen_Loader. Orchestrates the hooks of the plugin.
	 * - Couponsgen_i18n. Defines internationalization functionality.
	 * - Couponsgen_Admin. Defines all hooks for the admin area.
	 * - Couponsgen_Public. Defines all hooks for the public side of the site.
	 *
	 * Create an instance of the loader which will be used to register the hooks
	 * with WordPress.
	 *
	 * @since    1.0.0
	 * @access   private
	 */
	private function load_dependencies() {

		/**
		 * The class responsible for orchestrating the actions and filters of the
		 * core plugin.
		 */
		require_once plugin_dir_path( dirname( __FILE__ ) ) . 'includes/class-couponsgen-loader.php';

		/**
		 * The class responsible for defining internationalization functionality
		 * of the plugin.
		 */
		require_once plugin_dir_path( dirname( __FILE__ ) ) . 'includes/class-couponsgen-i18n.php';

		/**
		 * The class responsible for defining all actions that occur in the admin area.
		 */
		require_once plugin_dir_path( dirname( __FILE__ ) ) . 'admin/class-couponsgen-admin.php';

		/**
		 * The class responsible for defining all actions that occur in the public-facing
		 * side of the site.
		 */
		require_once plugin_dir_path( dirname( __FILE__ ) ) . 'public/class-couponsgen-public.php';

		$this->loader = new Couponsgen_Loader();

	}

	/**
	 * Define the locale for this plugin for internationalization.
	 *
	 * Uses the Couponsgen_i18n class in order to set the domain and to register the hook
	 * with WordPress.
	 *
	 * @since    1.0.0
	 * @access   private
	 */
	private function set_locale() {

		$plugin_i18n = new Couponsgen_i18n();

		$this->loader->add_action( 'plugins_loaded', $plugin_i18n, 'load_plugin_textdomain' );

	}

	/**
	 * Register all of the hooks related to the admin area functionality
	 * of the plugin.
	 *
	 * @since    1.0.0
	 * @access   private
	 */
	private function define_admin_hooks() {

		$plugin_admin = new Couponsgen_Admin( $this->get_plugin_name(), $this->get_version() );

		$this->loader->add_action( 'admin_enqueue_scripts', $plugin_admin, 'enqueue_styles' );
		$this->loader->add_action( 'admin_enqueue_scripts', $plugin_admin, 'enqueue_scripts' );

                $this->loader->add_action( 'admin_menu', $plugin_admin, 'add_plugin_admin_menu' );
                $this->loader->add_action('wp_dashboard_setup', $plugin_admin, 'couponsgen_add_dashboard_widget');
                // Add Settings link to the plugin
                $plugin_basename = plugin_basename( plugin_dir_path( __DIR__ ) . $this->plugin_name . '.php' );
                $this->loader->add_filter( 'plugin_action_links_' . $plugin_basename, $plugin_admin, 'add_action_links' );
	}

	/**
	 * Register all of the hooks related to the public-facing functionality
	 * of the plugin.
	 *
	 * @since    1.0.0
	 * @access   private
	 */
	private function define_public_hooks() {

                require_once plugin_dir_path( dirname( __FILE__ ) ) . 'includes/class-couponsgen-loader.php';

		$plugin_public = new Couponsgen_Public( $this->get_plugin_name(), $this->get_version() );

		$this->loader->add_action( 'wp_enqueue_scripts', $plugin_public, 'enqueue_styles' );
		$this->loader->add_action( 'wp_enqueue_scripts', $plugin_public, 'enqueue_scripts' );
	}

	/**
	 * Run the loader to execute all of the hooks with WordPress.
	 *
	 * @since    1.0.0
	 */
	public function run() {
		$this->loader->run();
	}

	/**
	 * The name of the plugin used to uniquely identify it within the context of
	 * WordPress and to define internationalization functionality.
	 *
	 * @since     1.0.0
	 * @return    string    The name of the plugin.
	 */
	public function get_plugin_name() {
		return $this->plugin_name;
	}

	/**
	 * The reference to the class that orchestrates the hooks with the plugin.
	 *
	 * @since     1.0.0
	 * @return    Couponsgen_Loader    Orchestrates the hooks of the plugin.
	 */
	public function get_loader() {
		return $this->loader;
	}

	/**
	 * Retrieve the version number of the plugin.
	 *
	 * @since     1.0.0
	 * @return    string    The version number of the plugin.
	 */
	public function get_version() {
		return $this->version;
	}
}

Can someone please help?