xsjs 500 internal server error

Hi

I'm trying to create my first XSJS file and when trying to run it I am getting "500 Internal server error"

500.png

Here is the code that I am trying to execute:

itsm.png

var destination_package = "itsm.services";
var destination_name = "Destination";
var custnum = $.request.body.asString();
var essai = custnum.toString().replace("\r", "").replace("\n", "").replace("\t", "");
essai = JSON.parse(essai);
var Prioritytickt = essai.Prioritytickt;

try {
	var dest = $.net.http.readDestination(destination_package, destination_name);
	var client = new $.net.http.Client();
	var req = new $.web.WebRequest($.net.http.GET, "MessageResultSet?$format=json"); //Entity Set 
	client.request(req, dest);
	var response = client.getResponse();

	$.response.contentType = "application/json";
	var result = response.body.asString();
	var jsonResult = JSON.parse(result);
	var chatbotResponse;

	if (jsonResult.d.results.length > 0) {

		if (Prioritytickt === "2") {
			chatbotResponse = "Here are the high priority tickets ";
		}
		if (Prioritytickt === "3") {
			chatbotResponse = "Here are the medium priority tickets ";
		}
		if (Prioritytickt === "4") {
			chatbotResponse = "Here are the low priority tickets ";
		}
		if (Prioritytickt === "All") {
			chatbotResponse = "List of all the tickets ";
		}

		if (Prioritytickt !== "All") {
			var ticketdetails = jsonResult.d.results.filter(function(hero) {
				return hero.Priority === Prioritytickt;
			});
			for (var i = 0; i < ticketdetails.length; i++) {

				chatbotResponse += ticketdetails[i].ObjectId;
				if (i < ticketdetails.length - 1) {
					chatbotResponse += ", ";
				}

			}
		} else {
			for (var i = 0; i < jsonResult.d.results.length; i++) {

				chatbotResponse += jsonResult.d.results[i].ObjectId;
				if (i < jsonResult.d.results.length - 1) {
					chatbotResponse += ", ";
				}

			}
		}

		var output = {
			replies: [{
				type: 'text',
				content: chatbotResponse
   					}],

			conversation: {
				memory: chatbotResponse
			}
		};
	} 
	var body = JSON.stringify(output);
	$.response.contentType = 'application/json';
	$.response.setBody(body);
	$.response.status = $.net.http.OK;

} catch (e) {
	$.response.contentType = "text/plain";
	$.response.setBody(e.message);
}

Please advice.

Regards,

Florence