Upload data to thingspeak.com using wifi module ESP8266

Projects Networking, Protocols, and Devices
1

I have an ESP8266 that is working with AT commands on Arduino MEGA using serial monitor and an bare minimum sketch (empty sketch) with baud rate 115200, TX pin 1, RX pin 0. But I want to use this code to upload data to thingspeak.com using an API key but it is not working. I tried many solutions but nothing. Is something wrong with this code?

Note: This code should be a part of another code on arduino MEGA

#include <SoftwareSerial.h>

// LED 
int ledPin = 13;
int sensor_pin=A0;  // variable for sensor
float sample=0;
float bat_volt =0;     // for temperature

// replace with your channel's thingspeak API key
String apiKey = "DUT8RMTFY2B1XCAF";

// connect 1 to TX of Serial USB
// connect 0 to RX of serial USB
SoftwareSerial ser(0,1); // RX, TX

// this runs once
void setup() {                
  // initialize the digital pin as an output.
  pinMode(ledPin, OUTPUT);    

  // enable debug serial
  Serial.begin(9600); 
  // enable software serial
  ser.begin(115200);
  
  // reset ESP8266
  ser.println("AT+RST");
}


// the loop 
void loop() {
  
  // blink LED on board
  digitalWrite(ledPin, HIGH);   
  delay(200);               
  digitalWrite(ledPin, LOW);

  voltage();
  esp_8266();
}
void voltage()
{
    sample=0; 
  for(int i=0;i<150;i++)
  {
    sample+=analogRead(sensor_pin);  //read the value from the sensor
    delay(2);
  }
  sample=sample/150; 
  bat_volt = sample*(4.76/1024)*(12/2); // R1+R2/R2 // R1=10k and R2=2k

 
  
}
void esp_8266()
{
 // convert to string
  char buf[32];
  String strVolt = dtostrf( bat_volt, 4, 1, buf);
  Serial.print(strVolt);
  Serial.println(" V");
  // TCP connection
  String cmd = "AT+CIPSTART=\"TCP\",\"";
  cmd += "184.106.153.149"; // api.thingspeak.com
  cmd += "\",80";
  ser.println(cmd);
   
  if(ser.find("Error")){
    Serial.println("AT+CIPSTART error");
    return;
  }
  
  // prepare GET string
  String getStr = "GET /update?api_key=";
  getStr += apiKey;
  getStr +="&field1=";
  getStr += String(strVolt);
  getStr += "\r\n\r\n";

  // send data length
  cmd = "AT+CIPSEND=";
  cmd += String(getStr.length());
  ser.println(cmd);

  if(ser.find(">")){
    ser.print(getStr);
  }
  else{
    ser.println("AT+CIPCLOSE");
    // alert user
    Serial.println("AT+CIPCLOSE");
  }
    
  // thingspeak needs 15 sec delay between updates
  delay(16000);  
}
2

I haven't gone through the code fully, but just saw a line and that just didn't do justice with the logic.

Serial.begin(9600);

SoftwareSerial ser(0,1); // RX, TX

Why are you using the hardware serial pins with software serial? It is meant to direct serial function on some other pins as pins 0,1 are not the best options as already discussed in various posts already.

So try and change this thing.....