tortabevono

This’s how I added custom data to orders (not products):

function my_custom_orders_api_fields( $order_data, $order ) {
    $order_data['your_custom_field_slug'] = get_post_meta( $order->id, 'your_custom_field_slug', true );

    return $order_data;
}
add_filter( 'woocommerce_api_order_response', 'my_custom_orders_api_fields', 10, 2 );

can you tell me which files you updated?

I put it into a custom plugin.