Something stupid

Apologies for the stupid question, but, I have a site running a child theme.
For some reason even the basic usage from the wiki, isn’t working. My meta box simply doesn’t show? What am I doing wrong?

functions.php

<?php
// Exit if accessed directly

add_action( 'cmb2_admin_init', 'cmb2_sample_metaboxes' );
/**
 * Define the metabox and field configurations.
 */
function cmb2_sample_metaboxes() {

	/**
	 * Initiate the metabox
	 */
	$cmb = new_cmb2_box( array(
		'id'            => 'test_metabox',
		'title'         => __( 'Test Metabox', 'cmb2' ),
		'object_types'  => array( 'page', ), // Post type
		'context'       => 'normal',
		'priority'      => 'high',
		'show_names'    => true, // Show field names on the left
		// 'cmb_styles' => false, // false to disable the CMB stylesheet
		// 'closed'     => true, // Keep the metabox closed by default
	) );

	// Regular text field
	$cmb->add_field( array(
		'name'       => __( 'Test Text', 'cmb2' ),
		'desc'       => __( 'field description (optional)', 'cmb2' ),
		'id'         => 'yourprefix_text',
		'type'       => 'text',
		'show_on_cb' => 'cmb2_hide_if_no_cats', // function should return a bool value
		// 'sanitization_cb' => 'my_custom_sanitization', // custom sanitization callback parameter
		// 'escape_cb'       => 'my_custom_escaping',  // custom escaping callback parameter
		// 'on_front'        => false, // Optionally designate a field to wp-admin only
		// 'repeatable'      => true,
	) );

	// URL text field
	$cmb->add_field( array(
		'name' => __( 'Website URL', 'cmb2' ),
		'desc' => __( 'field description (optional)', 'cmb2' ),
		'id'   => 'yourprefix_url',
		'type' => 'text_url',
		// 'protocols' => array('http', 'https', 'ftp', 'ftps', 'mailto', 'news', 'irc', 'gopher', 'nntp', 'feed', 'telnet'), // Array of allowed protocols
		// 'repeatable' => true,
	) );

	// Email text field
	$cmb->add_field( array(
		'name' => __( 'Test Text Email', 'cmb2' ),
		'desc' => __( 'field description (optional)', 'cmb2' ),
		'id'   => 'yourprefix_email',
		'type' => 'text_email',
		// 'repeatable' => true,
	) );

	// Add other metaboxes as needed

}

if ( !defined( 'ABSPATH' ) ) exit;
// BEGIN ENQUEUE PARENT ACTION
// AUTO GENERATED - Do not modify or remove comment markers above or below:

if ( !function_exists( 'chld_thm_cfg_locale_css' ) ):
    function chld_thm_cfg_locale_css( $uri ){
        if ( empty( $uri ) && is_rtl() && file_exists( get_template_directory() . '/rtl.css' ) )
            $uri = get_template_directory_uri() . '/rtl.css';
        return $uri;
    }
endif;
add_filter( 'locale_stylesheet_uri', 'chld_thm_cfg_locale_css' );
         
if ( !function_exists( 'child_theme_configurator_css' ) ):
    function child_theme_configurator_css() {
        wp_enqueue_style( 'chld_thm_cfg_child', trailingslashit( get_stylesheet_directory_uri() ) . 'style.css', array(  ) );
    }
endif;

// // END ENQUEUE PARENT ACTION