Is it possible to access custom fields for orders, products, customers via WooCommerce REST API? If not natively, then what plugins or workarounds or hacks are out there that wo
As mentioned in the comment after WooCommerce creates an order via the API it will fire woocommerce_api_create_order
hook, you can make use of it.
Add the following code to your theme's functions.php file
add_action( 'woocommerce_api_create_order', 'my_woocommerce_api_create_order', 10, 2);
function my_woocommerce_api_create_order( $order_id, $data ) {
// $data contains the data was posted, add code to extract the required
// fields and process it as required
}
Similarly look at the code in plugins/woocommerce/includes/api/*.php
files, find the suitable action or filter hook for the end point and use it.