WooCommerce issue with display PHP of custom field data

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I got this example for another Stack post]1. It was to add a barcode field to a WooCommerce product. The code worked in creating it, but the code to display it was another story. Threw a boolean error instead. Due to the call on member function 'get_meta'. This is the code from that post:

$product = wc_get_product( $product_id );
$product->get_meta( '_variable_billing' );

What would be proper code to eliminate the error? Here's the rest of the code from that post:

//Add barcode to the product inventory tab
add_action('woocommerce_product_options_inventory_product_data','add_barcode');
function add_barcode(){
    global $woocommerce,$post;
    woocommerce_wp_text_input(
        array(
            'id'          => '_barcode',
            'label'       => __('Barcode','woocommerce'),
            'placeholder' => 'Scan Barcode',
            'desc_tip'    => 'true',
            'description' => __('Scan barcode.','woocommerce')
        ));
}
//Save Barcode Field
function add_barcode_save($post_id){
    if(isset($_POST['_barcode'])){
        update_post_meta($post_id,'_barcode',sanitize_text_field($_POST['_barcode']));
    }else{
        delete_meta_data($post_id,'_barcode',sanitize_text_field($_POST['_barcode']));
    }
}
add_action('woocommerce_process_product_meta','add_barcode_save');
//Set POS Custom Code
function pos_barcode_field(){return '_barcode';}
add_filter('woocommerce_pos_barcode_meta_key','pos_barcode_field');