Display product custom field value on order items in WooCommerce admin orders

On Woocommerce, with the code below I have been able to add a custom field inside my general product options tabs with a textbox option. I also need to display this custom field on my order pages in a custom column in my order items detail page (the page in my admin area where I can see which products my customer bought).

Here is my code:

// Add custom column headers here
add_action('woocommerce_admin_order_item_headers', 'my_woocommerce_admin_order_item_headers');
function my_woocommerce_admin_order_item_headers() {
    $column_name = 'Plek';  
    echo '<th data-sort="float" style="text-align: right;" >' . $column_name . '</th>';
}

// Add custom column values here
add_action('woocommerce_admin_order_item_values', 'my_woocommerce_admin_order_item_values', 10, 3);
function my_woocommerce_admin_order_item_values($_product, $item, $item_id = null) {
    // get the post meta value from the associated product
    // $value = get_post_meta($_product->post->ID, '_custom_field_name', 1);
    $value = array_shift( wc_get_product_terms( $_product->post->ID, 'locatie', array( 'fields' => 'names' ) ) );
    echo '<td>' . $value . '</td>';
}

// Display order notes Fields
add_action( 'woocommerce_product_options_general_product_data', 'pans_woo_add_custom_general_fields' );
function pans_woo_add_custom_general_fields() {  global $woocommerce, $post;
    echo '<div class="pans_ta_options_group">';
    woocommerce_wp_textarea_input( array(
        'id'          => 'plek',
        'label'       => __( 'plek', 'woocommerce' ),
        'placeholder' => 'Alleen zichtbaar voor Admins.',   
    )  );
    echo '</div>';
}

// Save order note Fields
add_action( 'woocommerce_process_product_meta', 'pans_woo_add_custom_general_fields_save' );
function pans_woo_add_custom_general_fields_save( $post_id ){  
    $woocommerce_textarea = $_POST['plek']; 
    if( !empty( $woocommerce_textarea ) ) 
        update_post_meta( $post_id, 'plek', sanitize_textarea_field( $woocommerce_textarea ) );
}

The Product custom field value is displayed and saved correctly inside my general product options tabs (Product admin pages).

I also managed to get the column name done inside the order detail page.

But I am not able to display this product custom field value. Can anyone please give me some suggestions or help how to fix this?

What am I doing wrong?

I Have revisited your code as there are some errors and some outdated things in your code (Since WooCommerce 3). So try instead the following that will display your 'Plek' product custom field value on admin order pages:

// Add custom column headers to admin order pages
add_action('woocommerce_admin_order_item_headers', 'my_woocommerce_admin_order_item_headers');
function my_woocommerce_admin_order_item_headers() {
    $column_name = 'Plek';  
    echo '<th data-sort="float" style="text-align: right;" >' . $column_name . '</th>';
}

// Add custom column values to admin order pages
add_action('woocommerce_admin_order_item_values', 'my_woocommerce_admin_order_item_values', 10, 3);
function my_woocommerce_admin_order_item_values($product, $item, $item_id = null) {
    // get the product meta value from the associated product
    $value = $product->get_meta('plek');
    echo '<td>' . $value . '</td>';
}

// Display 'plek' custom fields on admin product pages
add_action( 'woocommerce_product_options_general_product_data', 'pans_woo_add_custom_general_fields' );
function pans_woo_add_custom_general_fields() {  
	global $post;
    echo '<div class="pans_ta_options_group">';
	
    woocommerce_wp_textarea_input( array(
        'id'          => 'plek',
        'label'       => __( 'plek', 'woocommerce' ),
        'placeholder' => 'Alleen zichtbaar voor Admins.',   
    )  );
	
    echo '</div>';
}

// Save 'plek' product custom Fields
add_action('woocommerce_admin_process_product_object', 'pans_woo_product_custom_field_save');
function pans_woo_product_custom_field_save( $product ) { 
    if( isset( $_POST['plek'] ) ) {
        $product->update_meta_data( 'plek', sanitize_textarea_field( $_POST['plek'] ) );
	}
}

Code goes in function.php file of your active child theme (or active theme). Tested and works