Updates to Future Payment Sample

- Renamed CorrelationId to ClientMetadataId
- Updated Source and Docs

sample/payments/CreateFuturePayment.php

@@ -59,8 +59,9 @@ $payment->setIntent("authorize")
 // authorization code from mobile sdk
 $authorizationCode = 'EJfRuAqXEE95pdVMmOym_mftTbeJD03RBX-Zjg9pLCAhdLqLeRR6YSKTNsrbQGX7lFoZ3SxwFyxADEZbBOxpn023W9SA0JzSQAy-9eLdON5eDPAyMyKlHyNVS2DqBR2iWVfQGfudbd9MDoRxMEjIZbY';
 
-// correlation id from mobile sdk
-$correlationId = '123123456';
+// Client Metadata id from mobile sdk
+// For more information look for PayPal-Client-Metadata-Id in https://developer.paypal.com/docs/api/#authentication--headers
+$clientMetadataId = '123123456';
 
 try {
     // Exchange authorization_code for long living refresh token. You should store
@@ -81,7 +82,7 @@ try {
     // url to which the buyer must be redirected to
     // for payment approval
     // Please note that currently future payments works only with PayPal as a funding instrument.
-    $payment->create($apiContext, $correlationId);
+    $payment->create($apiContext, $clientMetadataId);
 
 } catch (Exception $ex) {
     ResultPrinter::printError("Future Payment", "Payment", null, $request, $ex);