not getting the graph

i am uploading a code for mq135 gas sensor and node mcu. But the graph is not displayed in Thingspeak.any one can help please?the code is here

#include<ThingSpeak.h>
#include <WiFiClient.h>;
#include <SPI.h>
#include "MQ135.h"
#include <ESP8266WiFi.h>
const char  *apiKey = "1CUJEV41WNM7WHHP"; // Enter your Write API key from ThingSpeak
const char *ssid = "Harrin"; // replace with your wifi ssid and wpa2 key
const char *pass = "harrin20";
const char* server = "api.thingspeak.com";
WiFiClient client;
unsigned long myChannelNumber = 876579;
      byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};
     #define VOLTAGE_MAX 5.0
     #define VOLTAGE_MAXCOUNTS 1023.0
 
void setup() {
  Serial.begin(9600);
delay(10);
Serial.println("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, pass);
 ThingSpeak.begin(client);
}

void loop() {
  // read the input on analog pin 0:
  int sensorValue = analogRead(A0);
  // Convert the analog reading 
  // On Arduino:  0 - 1023 maps to 0 - 5 volts
  // On ESP8266:  0 - 1023 maps to 0 - 1 volts
  // On Particle: 0 - 4095 maps to 0 - 3.3 volts
  float voltage = sensorValue * (VOLTAGE_MAX / VOLTAGE_MAXCOUNTS);
  Serial.print(voltage);
  Serial.println();
    
  delay(10000); // ThingSpeak will only accept updates every 15 seconds
  ThingSpeak.writeField(myChannelNumber, 1,voltage, apiKey); //Update in ThingSpeak
  delay (100);

[Walter Roberson]

darova: note that ThinkSpeak is a Mathworks product; https://www.mathworks.com/products/thingspeak.html

[Vinod]

Have you confirmed your device is able to the internet? What do you see in the serial monitor?