Ajouter un produit gratuit dans chaque commande Woocommerce (après paiement)

functions.php

<?php

add_filter( 'woocommerce_get_settings_products', 'woo_settings_free_products' );
function woo_settings_free_products( $settings ) {
	$settings[] = array(
		'name' => __( 'Produits gratuits', 'woocommerce' ),
		'type' => 'title',
		'id'   => 'free_products'
	);
    $settings[] = array(
        'name' => __( 'Produits gratuits à ajouter à chaque commande', 'woocommerce' ),
        'type' => 'text',
		'id'   => 'free_products',
		'desc' => 'Saisissez les IDs des produits, séparés par une virgule',
		'default' => '',
	);
	$settings[] = array(
        'type' => 'sectionend',
        'id'   => 'free_products'
    );
	return $settings;
}
add_action( 'woocommerce_payment_complete','maybe_add_free_product_after_order_complete', 100 );
function maybe_add_free_product_after_order_complete( $order_id ) {
	$free_products = get_option( 'free_products' );
	if ( empty( $free_products ) ) {
		return;
	}
	$free_products = explode( ',', $free_products );
	$free_products = array_filter( $free_products );
	$free_products = array_map( 'trim', $free_products );
	$free_products = array_map( 'intval', $free_products );
	if ( empty( $free_products ) ) {
		return;
	}
	
	$order = wc_get_order( $order_id );
	if ( is_wp_error( $order ) ) {
		return;
	}
	foreach ( $free_products as $product ) {
		$product_item = wc_get_product( $product );
		$order->add_product( $product_item, 1, array( 'total' => 0, 'subtotal' => 0 ) );
	}
}