fix: PayPal webhooks: 退款 invoice number

webht/third_party/paypal/controllers/index.php

@@ -658,6 +658,7 @@ class Index extends CI_Controller {
                 $post_data->mc_fee = $post_data->resource->transaction_fee->value;
                 break;
             case 'PAYMENT.SALE.REFUNDED':
+                $pn_invoice = $post_data->resource->invoice_number;
                 $pn_payment_status = 'Refunded';
                 $pn_mc_gross = '-' . $post_data->resource->amount->total;
                 $post_data->parent_txn_id = $post_data->resource->sale_id;