I am using Dialogflow es version and want to use Dialogflow phone gateway integration so a little bit of background, I am now able to integrate it and I got us a phone number and all the basic things are working but if I use custom webhook it is not working currently I am categorizing like this in the webhook node.js function

if (agent.requestSource == 'GOOGLE_TELEPHONY') {
        agent.add('test test');
}else{
        agent.add('not telephony');
}

but it is not working any suggestions?

note If I add something in the dialogflow console itself it is working but not with the custom webhook code.