amazon web services – mqtt error code RC = -1 connecting while esp32 to aws

I am going to establish a mqtt connection to aws. DHT senstor reading must be sent from esp32 to aws. How can I fix the error RC = -1 when connecting esp32 to aws. I receive this error in serial monitor :
Attempting MQTT connection…failed, rc=-1 try again in 5 seconds

What can be the reaon?

My code is as follows:

#include "SPIFFS.h"
#include <WiFiClientSecure.h>
#include <PubSubClient.h>
#include <DHT.h>  // library for getting data from DHT


// Enter your WiFi ssid and password
const char* ssid = "TP-Link_DBCA"; //Provide your SSID
const char* password = "44388027"; // Provide Password
const char* mqtt_server = "a3k7086cinb3bt-ats.iot.us-west-2.amazonaws.com"; // Relace with your MQTT END point
const int   mqtt_port = 8883;

String Read_rootca;
String Read_cert;
String Read_privatekey;
#define BUFFER_LEN 256
long lastMsg = 0;
char msg(BUFFER_LEN);
int Value = 0;
byte mac(6);
char mac_Id(18);
int count = 1;

WiFiClientSecure espClient;
PubSubClient client(espClient);



#define DHTPIN 4        //pin where the DHT22 is connected 
DHT dht(DHTPIN, DHT11);

void setup_wifi() {
  delay(10);
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  randomSeed(micros());

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived (");
  Serial.print(topic);
  Serial.print(") ");
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload(i));
  }
  Serial.println();
}
void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Create a random client ID
    String clientId = "ESP32-";
    clientId += String(random(0xffff), HEX);
    // Attempt to connect
    if (client.connect(clientId.c_str())) {
      Serial.println("connected");
      // Once connected, publish an announcement...
      client.publish("ei_out", "hello world");
      // ... and resubscribe
      client.subscribe("ei_in");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void setup() {
  Serial.begin(115200);
  dht.begin();
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(2, OUTPUT);
  setup_wifi();
  delay(1000);
  //=============================================================
  if (!SPIFFS.begin(true)) {
    Serial.println("An Error has occurred while mounting SPIFFS");
    return;
  }
  //=======================================
  //Root CA File Reading.
  File file2 = SPIFFS.open("/AmazonRootCA1.pem", "r");
  if (!file2) {
    Serial.println("Failed to open file for reading");
    return;
  }
  Serial.println("Root CA File Content:");
  while (file2.available()) {
    Read_rootca = file2.readString();
    Serial.println(Read_rootca);
  }
  //=============================================
  // Cert file reading
  File file4 = SPIFFS.open("/certificate.pem.crt.txt", "r");
  if (!file4) {
    Serial.println("Failed to open file for reading");
    return;
  }
  Serial.println("Cert File Content:");
  while (file4.available()) {
    Read_cert = file4.readString();
    Serial.println(Read_cert);
  }
  //=================================================
  //Privatekey file reading
  File file6 = SPIFFS.open("/private.pem.key", "r");
  if (!file6) {
    Serial.println("Failed to open file for reading");
    return;
  }
  Serial.println("privateKey File Content:");
  while (file6.available()) {
    Read_privatekey = file6.readString();
    Serial.println(Read_privatekey);
  }
  //=====================================================

  char* pRead_rootca;
  pRead_rootca = (char *)malloc(sizeof(char) * (Read_rootca.length() + 1));
  strcpy(pRead_rootca, Read_rootca.c_str());

  char* pRead_cert;
  pRead_cert = (char *)malloc(sizeof(char) * (Read_cert.length() + 1));
  strcpy(pRead_cert, Read_cert.c_str());

  char* pRead_privatekey;
  pRead_privatekey = (char *)malloc(sizeof(char) * (Read_privatekey.length() + 1));
  strcpy(pRead_privatekey, Read_privatekey.c_str());

  Serial.println("================================================================================================");
  Serial.println("Certificates that passing to espClient Method");
  Serial.println();
  Serial.println("Root CA:");
  Serial.write(pRead_rootca);
  Serial.println("================================================================================================");
  Serial.println();
  Serial.println("Cert:");
  Serial.write(pRead_cert);
  Serial.println("================================================================================================");
  Serial.println();
  Serial.println("privateKey:");
  Serial.write(pRead_privatekey);
  Serial.println("================================================================================================");

  espClient.setCACert(pRead_rootca);
  espClient.setCertificate(pRead_cert);
  espClient.setPrivateKey(pRead_privatekey);

  client.setServer(mqtt_server, mqtt_port);
  client.setCallback(callback);

  //====================================================================================================================
  WiFi.macAddress(mac);
  snprintf(mac_Id, sizeof(mac_Id), "%02x:%02x:%02x:%02x:%02x:%02x",
           mac(0), mac(1), mac(2), mac(3), mac(4), mac(5));
  Serial.print(mac_Id);
  //=====================================================================================================================
  delay(2000);
}


void loop() {
  float h = 80;   // Reading Temperature form DHT sensor
  float t = 22.5;      // Reading Humidity form DHT sensor
  float tF = (t * 1.8) + 32;
  if (isnan(h) || isnan(t))
  {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }
  if (!client.connected()) {
    reconnect();
  }
  client.loop();

  long now = millis();
  if (now - lastMsg > 2000) {
    lastMsg = now;
    //=============================================================================================
    String macIdStr = mac_Id;
    String Temprature = String(t);
    String Humidity = String(h);
    snprintf (msg, BUFFER_LEN, "{"mac_Id" : "%s", "Temprature" : %s, "Humidity" : "%s"}", macIdStr.c_str(), Temprature.c_str(), Humidity.c_str());
    Serial.print("Publish message: ");
    Serial.print(count);
    Serial.println(msg);
    client.publish("temp/", msg);
    count = count + 1;
    //================================================================================================
  }
  digitalWrite(2, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                       // wait for a second
  digitalWrite(2, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                       // wait for a second
}```