App to phone call using Sinch Rest Api

Question

I am using sinch rest api for phone calling everthing is working fine and my problem is how to change the audio (wav) file the default file is mentioned in text:http://www.thehotline.co/content/prompts/v2/1greeting_b.wav but if i change the audio file to http://www.wav-sounds.com/cartoon/bugsbunny1.wav the audio file is not playing instead it read the file path...

[POST] https://callingapi.sinch.com/v1/callouts
   {
  "method" : "ttsCallout",
   "ttsCallout" :
   {
   "cli" : "46000000000",
   "destination" : { "type" : "number", "endpoint" : "46000000001" },
   "domain" : "pstn",
   "custom" : "customData",
    "locale" : "en-US",
    "text" : "http://www.thehotline.co/content/prompts/v2/1greeting_b.wavss"
   }
 }

Thanks...