Updated Invoice Object to retrieve payments and refunds

- getPaymentDetails is now getPayments
- getRefundDetails is now getRefunds
- Updated Sample to Get Invoice at the end of each operation
- Updated Tests

sample/invoice/RemindInvoice.php

@@ -36,3 +36,19 @@ try {
 
 ResultPrinter::printResult("Remind Invoice", "Invoice", null, $notify, null);
 
+// ### Retrieve Invoice
+// Retrieve the invoice object by calling the
+// static `get` method
+// on the Invoice class by passing a valid
+// Invoice ID
+// (See bootstrap.php for more on `ApiContext`)
+try {
+    $invoice = Invoice::get($invoice->getId(), $apiContext);
+} catch (Exception $ex) {
+    ResultPrinter::printError("Get Invoice (Not Required - For Sample Only)", "Invoice", $invoice->getId(), $invoice->getId(), $ex);
+    exit(1);
+}
+
+ResultPrinter::printResult("Get Invoice (Not Required - For Sample Only)", "Invoice", $invoice->getId(), $invoice->getId(), $invoice);
+
+return $invoice;