Client is not defined in a Request API

Hi. Im building an app to bring information from an crm but I got this error: 

app.js:484 Uncaught ReferenceError: client is not defined

This is my code in app.js: 

$(document).ready( function() {
    app.initialized()
        .then(function(_client) {
          var client = _client;
          client.events.on('app.activated',
            function() {
                client.data.get('contact')
                    .then(function(data) {
                        $('#apptext').text("Ticket created by " + data.contact.name);
                    })
                    .catch(function(e) {
                        console.log('Exception - ', e);
                    });
                    client.events.on("ticket.customFieldChanged", eventCallback);
        });

    });
});
var eventCallback = function(event) {
  var customField = event.data; // { cf_single_line: { new: "1234", old: undefined } }
  var test = customField.cf_numero_fp.new;
var headers = {"Authorization": "eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJhYjQwMzIwM2MzNDE0MjYyOWVmNjcyMTUwZGQ4OGUxNCIsInJvbGUiOiJCUUFBQVFBQUFBQUFBQUFBQUFBQUFBQUFBQUE9IiwibmFtZSI6IkZyZXNoZGVzayBBUEkiLCJleHAiOjE1NzI4ODYxNjB9.xrYMTEoVfPSceb1HG6znsrgL5P617xiseyfy6fQoKB8"};
  var options = { headers: headers };
  var url = "https://ngapi.freedompop.mx/api/freshdesk/phone/" + test;
  client.request.get(url, options)
  .then (
  function(data) {
    console.log('Esto funciona');
    //client.interface.trigger("setValue", { id: "cf_number", value:data.cf_serie_sim_iccid})
    //client.interface.trigger("setValue", { id: "cf_number", value:data.iccid})
  },
  function(error) {
    console.log(error);
  });
}

I will be grateful if you can help me. 

Thanks