restore woocommerce refund field (WooCommerce 3.6+)

gistfile1.txt

add_action('admin_head', 'rwk_refund_field', 999);


function rwk_refund_field() {
	$currentPostType = get_post_type();
 // filter for shop only
	if( $currentPostType != 'shop_order' ) {
		return;
	}
// remove the blocker
?>
	<script>
		(function($){
			$(document).ready(function(){
				$('#refund_amount').removeAttr('readonly');
			});
		})(jQuery);
	</script>
<?php
}