How to add custom fields to the Shop as Client PRO add-on ajax call

shop_as_client_pro_customer_data.php

<?php

/* Add this to you (child-)theme functions.php file */

add_filter( 'shop_as_client_pro_customer_data', 'my_shop_as_client_pro_customer_data', 10, 3 );
function my_shop_as_client_pro_customer_data( $data, $customer = null, $order = null ) {
	if ( $customer ) {
		//Getting a customer object
		//Custom checkout field with id "billing_xpto"
		$data['billing']['xpto'] = $customer->get_meta( 'billing_xpto' );
		//Custom checkout field with id "shipping_xpto"
		$data['shipping']['xpto'] = $customer->get_meta( 'shipping_xpto' );
		//Custom field "whatever" loaded into the custom checkout with id ""billing_whatever"
		$data['billing']['whatever'] = $customer->get_meta( 'whatever' );
		//Custom checkout field with id "field_id" that is neither from billing nor shipping
		$data['custom']['field_id'] = $customer->get_meta( 'custom_field_meta' );
		//Return the data
	} elseif ( $order ) {
		//Getting a order object
		//Custom checkout field with id "billing_xpto" fetched from order meta field "_billing_xpto"
		$data['billing']['xpto'] = $order->get_meta( '_billing_xpto' );
		//Custom checkout field with id "field_id", from order, that is neither from billing nor shipping, fetched from order meta field "custom_field_meta"
		$data['custom']['field_id'] = $order->get_meta( 'custom_field_meta' );
	}
	return $data;
}