Override an order line item's SKU using the compounded SKU when using WooCommerce's REST API

override-sku-in-wc-rest-api.php

<?php
/**
 * Filters the REST response for shop order object
 */
add_filter( 'woocommerce_rest_prepare_shop_order_object', function( $response ) {

	if ( ! function_exists( 'mkl_pc' ) ) return $response;

	$configurator = null;
	if ( ! isset( $response->data['line_items'] ) ) return $response;
	$sku_key = mkl_pc( 'settings')->get( 'sku_label', __( 'SKU', 'product-configurator-for-woocommerce' ) );
	foreach( $response->data['line_items'] as $item_id => $line_item ) {
		if ( isset( $line_item['meta_data'] ) ) {
			foreach( $line_item['meta_data'] as $ind => $meta_data ) {
				// Add the configurator to the first line
				if ( $sku_key === $meta_data['key'] ) {
					$response->data['line_items'][$item_id]['sku'] = $meta_data['value'];
					continue 2;
				}
			}
		}
	}

	return $response;
} );