I cannot get custom fields to display, thanks

I have read and repeatedly tried to implement the code on this page to display fields:

https://docs.metabox.io/displaying-fields/

but it just isn't working.

Here is the code from metabox for creating my metabox:

function coaching_lesson_meta_box( $meta_boxes ) {
    $prefix = 'prefix-';

    $meta_boxes[] = array(
        'id' => 'coaching_lessons-metabox',
        'title' => esc_html__( 'Coaching Lesson Components', 'metabox-online-generator' ),
        'post_types' => array('post', 'page', 'coaching_program', 'coaching_lesson' ),
        'context' => 'after_title',
        'priority' => 'default',
        'autosave' => 'false',
        'fields' => array(
            array(
                'id' => $prefix . 'coaching_lesson_summary',
                'type' => 'textarea',
                'name' => esc_html__( 'Summary of Coaching Lesson', 'metabox-online-generator' ),
            ),

This is the code on my single-coaching_lesson.php page:

<?php astra_entry_before(); ?>

<article itemtype="https://schema.org/CreativeWork" itemscope="itemscope" id="post-<?php the_ID(); ?>" <?php post_class(); ?>>

    <?php astra_entry_top(); ?>

    <?php astra_entry_content_single();
    
    
 ?>

<?php 

$value = rwmb_meta( 'coaching_lesson_summary' );
echo $value;

?>

It just isn't showing on the page.

What am I doing wrong?

Thank you very much

Sean