postback.js

[{
    u 'postback': {
        u 'payload': u 'my postback string'
    },
    u 'recipient': {
        u 'id': 129283210520070
    },
    u 'sender': {
        u 'id': 1049549878444680
    },
    u 'timestamp': 1461963825480
}]