Trying to publish data from DHT22 Sensor from Arduino to ROS using rosserial

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I am using ROS Melodic and have followed the steps for the Hello World Tutorial, it works. I have also tried uploading a sample code for the DHT11 Sensore, it sends data but not exaclty what I want.

My code can be uploaded. However, when I run the rosrun rosserial_pyhon serial_node.py /dev/ttyACM0. It shows the message: " Unable to sync with device; possible link problem or link software version mismatch such as hydro rosserial_python with groovy Arduino".

#include "DHT.h"
#include <ros.h>
#include <sensor_msgs/Temperature.h>
#include <sensor_msgs/RelativeHumidity.h>

ros::NodeHandle nh;
sensor_msgs::Temperature temp_msg;
sensor_msgs::RelativeHumidity humidity_msg;
ros::Publisher pub_temp("temperature", &temp_msg);
ros::Publisher pub_humidity("humidity", &humidity_msg);

//Constants
#define DHTPIN 2     // what pin we're connected to
#define DHTTYPE DHT22   // DHT 22  (AM2302)
DHT dht(DHTPIN, DHTTYPE); //// Initialize DHT sensor for normal 16mhz Arduino

//Variables
int chk;
int hum;  //Stores humidity value
int temp; //Stores temperature value


void setup()
{
  nh.initNode();
  nh.advertise(pub_temp);
  nh.advertise(pub_humidity);
    Serial.begin(9600);
  dht.begin();

}

void loop()
{
    begn:delay(2000);
    //Read data and store it to variables hum and temp
    humidity_msg.relative_humidity = dht.readHumidity();
    temp_msg.temperature= dht.readTemperature();
    temp_msg.header.stamp = nh.now();
    humidity_msg.header.stamp = nh.now();
    //Print temp and humidity values to serial monitor
    pub_temp.publish( &temp_msg );
    pub_humidity.publish( &humidity_msg );
    delay(2000); //Delay 2 sec.
    nh.spinOnce();

}