Electrical – How to fix the error “Response code 0” to get “Response code 202” to bulk update a thingspeak channel

I am using this example:
https://www.mathworks.com/help/thingspeak/continuously-collect-data-and-bulk-update-a-thingspeak-channel-using-an-arduino-mkr1000-board-or-an-esp8266-board.html

According to the example I should be getting a "Response code 202".However, I am getting Response code 0. Therefore, I am not getting any thing on my thingspeak channel. My board is esp8266 thing dev.

My serial monitor displays this output:

Attempting to connect to SSID: Xperia Z_a769
Connected to wifi
SSID: Xperia Z_a769
IP Address: **********
signal strength (RSSI):-47 dBm
Response code:0

Why am I getting response code 0 ? How can I fix this issue to get data on thingspeak.com. Help please!!
I have attached my code below:

/* This example shows how to bulk update a ThingSpeak channel using an 
   Arduino MKR1000 or an ESP8266*/

 #include //Uncomment this library to work with ESP8266
 #include //Uncomment this library to work with ESP8266

 //#include // Comment this to work with ESP8266 board
//#include // Comment this to work with ESP8266 board

char jsonBuffer[500] = "["; // Initialize the jsonBuffer to hold data

char ssid[] = "Xperia Z_a769"; // Your network SSID (name)
char pass[] = "7c6761b56ed2"; // Your network password
WiFiClient client; // Initialize the WiFi client library

char server[] = "api.thingspeak.com"; // ThingSpeak Server

/* Collect data once every 15 seconds and post data to ThingSpeak channel 
once every 2 minutes */
unsigned long lastConnectionTime = 0; // Track the last connection time
unsigned long lastUpdateTime = 0; // Track the last update time
const unsigned long postingInterval = 120L * 1000L; // Post data every 2 
minutes
const unsigned long updateInterval = 15L * 1000L; // Update once every 15 
seconds

void setup() {
Serial.begin(9600);
// Attempt to connect to WiFi network
while (WiFi.status() != WL_CONNECTED) {
Serial.print("Attempting to connect to SSID: ");
Serial.println(ssid);
WiFi.begin(ssid, pass); // Connect to WPA/WPA2 network. Change this line if 
using open or WEP network
delay(10000); // Wait 10 seconds to connect
  }
  Serial.println("Connected to wifi");
  printWiFiStatus(); // Print WiFi connection information
  }

void loop() {
// If update time has reached 15 seconds, then update the jsonBuffer
if (millis() - lastUpdateTime >= updateInterval) {
updatesJson(jsonBuffer);
  }

 }

 // Updates the jsonBuffer with data
void updatesJson(char* jsonBuffer){
/* JSON format for updates paramter in the API
* This example uses the relative timestamp as it uses the "delta_t". If your 
device has a real-time clock, you can provide the absolute timestamp using 
the "created_at" parameter
* instead of "delta_t".
* "[{\"delta_t\":0,\"field1\":-70},{\"delta_t\":15,\"field1\":-66}]"
*/
// Format the jsonBuffer as noted above
strcat(jsonBuffer,"{\"delta_t\":");
 unsigned long deltaT = (millis() - lastUpdateTime)/1000;
 size_t lengthT = String(deltaT).length();
 char temp[4];
 String(deltaT).toCharArray(temp,lengthT+1);
 strcat(jsonBuffer,temp);
 strcat(jsonBuffer,",");
 long rssi = WiFi.RSSI();
  strcat(jsonBuffer, "\"field1\":");
 lengthT = String(rssi).length();
 String(rssi).toCharArray(temp,lengthT+1);
 strcat(jsonBuffer,temp);
 strcat(jsonBuffer,"},");
 // If posting interval time has reached 2 minutes, then update the 
 ThingSpeak channel with your data
  if (millis() - lastConnectionTime >= postingInterval) {
  size_t len = strlen(jsonBuffer);
  jsonBuffer[len-1] = ']';
  httpRequest(jsonBuffer);
 }
 lastUpdateTime = millis(); // Update the last update time
  }

 // Updates the ThingSpeakchannel with data
 void httpRequest(char* jsonBuffer) {
 /* JSON format for data buffer in the API
 * This example uses the relative timestamp as it uses the "delta_t". If 
   your device has a real-time clock, you can also provide the absolute 
   timestamp using the "created_at" parameter
   * instead of "delta_t".
   * "{\"write_api_key\":\"YOUR-CHANNEL-WRITEAPIKEY\",\"updates\": 
      [{\"delta_t\":0,\"field1\":-60},{\"delta_t\":15,\"field1\":200}, 
      {\"delta_t\":15,\"field1\":-66}]
   */
   // Format the data buffer as noted above
  char data[500] = "{\"write_api_key\":\"6OF022OLH2QM50TP\",\"updates\":"; 
   //Replace YOUR-CHANNEL-WRITEAPIKEY with your ThingSpeak channel write API 
   key
  strcat(data,jsonBuffer);
  strcat(data,"}");
  // Close any connection before sending a new request
  client.stop();
  String data_length = String(strlen(data)+1); //Compute the data buffer 
  length
  // POST data to ThingSpeak
  if (client.connect(server, 80)) {
  client.println("POST /channels/522490/bulk_update.json HTTP/1.1"); 
  //Replace YOUR-CHANNEL-ID with your ThingSpeak channel ID
  client.println("Host: api.thingspeak.com");
  client.println("User-Agent: mw.doc.bulk-update (Arduino ESP8266)");
  client.println("Connection: close");
  client.println("Content-Type: application/json");
  client.println("Content-Length: "+data_length);
  client.println();
  client.println(data);
 }
 else {
 Serial.println("Failure: Failed to connect to ThingSpeak");
}
 delay(15000); //Wait to receive the response
client.parseFloat();
String resp = String(client.parseInt());
Serial.println("Response code:"+resp); // Print the response code. 202 
                     indicates that the server has accepted the response
jsonBuffer[0] = '['; // Reinitialize the jsonBuffer for next batch of data
jsonBuffer[1] = '\0';
lastConnectionTime = millis(); // Update the last connection time
  }

  void printWiFiStatus() {
 // Print the SSID of the network you're attached to:
 Serial.print("SSID: ");
 Serial.println(WiFi.SSID());

 // Print your device IP address:
 IPAddress ip = WiFi.localIP();
 Serial.print("IP Address: ");
  Serial.println(ip);

 // Print the received signal strength:
 long rssi = WiFi.RSSI();
 Serial.print("signal strength (RSSI):");
 Serial.print(rssi);
 Serial.println(" dBm");
}