product_addons_meta_data.php

<?php 
/**
 * Get add-on metadata from each line item in the order
 * @param	$order_id
 * @param $metakey	The add-ons metakey (field label), usually prefixed by an underscore
 */
function prefix_get_addons_metadata_by_key( $order_id, $metakey=false ) {
	
	$order = wc_get_order( $order_id );
	$order_line_items = $order->get_items();

	foreach( $order_line_items as $line_item ) {

		// Here, we can iterate through all the meta for this line item
		$all_meta = $line_item->get_meta_data();
		if( $all_meta ) {
			foreach( $all_meta as $meta ) {
				$meta_id = $meta->id;
				$meta_key = $meta->key;
				$meta_value = $meta->value;
			}
		}
		
		// Here, we can get the value by a specific metakey
		if( $metakey ) {
			$meta_value = $line_item->get_meta( $metakey );
		}
		
	}
	
}