Update messages/whatsapp/send-mtm.php

Co-authored-by: Karl Lingiah <karl@superchilled.co.uk>

Author: SecondeJK

messages/whatsapp/send-mtm.php

@@ -18,7 +18,7 @@
  ],
 ];
 
-$sms = new \Vonage\Messages\MessageType\WhatsApp\WhatsAppCustom(
+$whatsApp = new \Vonage\Messages\MessageType\WhatsApp\WhatsAppCustom(
  TO_NUMBER,
  FROM_NUMBER,
  $custom