I have written code in the Arduino IDE to send messages to an NCP MQTT using an ESP32.

#include <WiFi.h>
#include <WiFiClientSecure.h>
#include <PubSubClient.h>

#define root_ca 
"-----BEGIN CERTIFICATE-----n" 
"MIIDuT**********************************************************n"    
"-----END CERTIFICATE-----n"

#define client_cert 
"-----BEGIN CERTIFICATE-----n" 
"MIIESj**********************************************************n"    
"-----END CERTIFICATE-----n"

#define private_key 
"-----BEGIN PRIVATE KEY-----n" 
"MIIEow**********************************************************n"              
"-----END PRIVATE KEY-----n"

const char* ssid = "5021";
const char* password = "12345678";
const char* mqtt_server = "ssl://msg01.cloudiot.ntruss.com";
const int mqtt_port = 8883;

There are discussions addressing the issue of mqtt_port, so I have checked both 8883 and 1883.

WiFiClientSecure espClient;
PubSubClient client(espClient);

long lastMsg = 0;
char msg[256];
int msgCount = 0;

void setup_wifi() {
  delay(10);
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED)
  {
    delay(500);
  }
}

I have confirmed that WiFi is connected properly.

void reconnect() {
  if (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    unsigned long startTime = millis();

    if (client.connect("arduinoClient")) {
      Serial.println("connected");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      delay(5000);
    }

    Serial.print("Connection attempt took ");
    Serial.print(millis() - startTime);
    Serial.println(" ms");
  }
}

The continuous occurrence of the rc=-2 error at this point suggests that there might be an issue with the key files or potentially with the communication protocol itself.

void setup() {
  Serial.begin(115200);
  setup_wifi();
  char *dest3;
  char *dest1;
  char *dest2;
  dest1 = (char *)malloc(sizeof(char) * (strlen(root_ca) + 1));
  strcpy(dest1, root_ca);
    dest2 = (char *)malloc(sizeof(char) * (strlen(client_cert) + 1));
  strcpy(dest2, client_cert);
    dest3 = (char *)malloc(sizeof(char) * (strlen(private_key) + 1));
  strcpy(dest3, private_key);
  espClient.setCACert(dest1);
  espClient.setCertificate(dest2); 
  espClient.setPrivateKey(dest3);
  client.setServer(mqtt_server, mqtt_port);
}

void loop() {
  if (!client.connected()) {
    reconnect();
  }
  if(client.connected() ) {
    Serial.print("Client connected");
  }
}

“I’ve been modifying my code based on various sources, and I’ve confirmed that WiFi is connected properly, but I keep encountering rc=-2 error. I’m unsure whether I need to adjust settings in the Arduino IDE or change settings in Windows. Please help.”