For iOS: The callback is received in delegateMessageReceived which is added in the file added in the above step. The response is a stringified JSON and can be used as per the requirement. code example

Example 1: Javascript object to JSON string

var person={"first_name":"Tony","last_name":"Hawk","age":31};
var personJSONString=JSON.stringify(person);

Example 2: json.stringify parameters

var person={"first_name":"Tony","last_name":"Hawk","age":31};
console.log(JSON.stringify(person , null , 4)); 
//Output:
> "{
    "first_name": "Tony",
    "last_name": "Hawk",
    "age": 31
}"