Update Invoicing Samples

sample/invoice/RemindInvoice.php

@@ -4,7 +4,8 @@
 // This sample code demonstrate how you can remind
 // an invoice to the payer
 
-require __DIR__ . '/../bootstrap.php';
+/** @var Invoice $invoice */
+$invoice = require 'SendInvoice.php';
 
 use PayPal\Api\Invoice;
 use PayPal\Api\Notification;
@@ -16,7 +17,7 @@ try {
     // on the Invoice class by passing a valid
     // Invoice ID
     // (See bootstrap.php for more on `ApiContext`)
-    $invoice = Invoice::get("INV2-W4LC-6QS9-JZ62-VE4P", $apiContext);
+    $invoice = Invoice::get($invoice->getId(), $apiContext);
 
     // ### Notification Object
     // This would send a notification to both merchant as well