TTGO T-Call ESP32 SIM800 http post request to server not successful

Hi all, I'm new to using esp(this is my first project actually) and I'm struggling to find out answer for my question.
I'm using the esp board to send data to rest api of my own deployed on Azure. The data sent is JSON.
If I use the onboard Wifi everything works fine and here is my code for this:

#include <WiFi.h>
#include <HTTPClient.h>

const char* ssid = "net";
const char* password = "23534534534";

//Your Domain name with URL path or IP address with path
const char* serverName = "http://*****.azurewebsites.net/api/v1/position_data";

// the following variables are unsigned longs because the time, measured in
// milliseconds, will quickly become a bigger number than can be stored in an int.
unsigned long lastTime = 0;
// Timer set to 10 minutes (600000)
//unsigned long timerDelay = 600000;
// Set timer to 5 seconds (5000)
unsigned long timerDelay = 5000;

void setup() {
  Serial.begin(115200);

  WiFi.begin(ssid, password);
  Serial.println("Connecting");
  while(WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("Connected to WiFi network with IP Address: ");
  Serial.println(WiFi.localIP());
 
  Serial.println("Timer set to 5 seconds (timerDelay variable), it will take 5 seconds before publishing the first reading.");
}

void loop() {
  //Send an HTTP POST request every 10 minutes
  if ((millis() - lastTime) > timerDelay) {
    //Check WiFi connection status
    if(WiFi.status()== WL_CONNECTED){
      WiFiClient client;
      HTTPClient http;
    
      // Your Domain name with URL path or IP address with path
      http.begin(client, serverName);
     
      // If you need an HTTP request with a content type: application/json, use the following:
      http.addHeader("Content-Type", "application/json");
      int httpResponseCode = http.POST("{\"latitude\":\"7777\",\"longitude\":\"7777\",\"altitude\":\"7777\",\"speed\":\"7777\",\"deviceId\":\"111112222200000\"}");
     
      Serial.print("HTTP Response code: ");
      Serial.println(httpResponseCode);
        
      // Free resources
      http.end();
    }
    else {
      Serial.println("WiFi Disconnected");
    }
    lastTime = millis();
  }
}

As I said when using Wifi everything works fine, but my goal is to use the onboard SIM800 module.
Here is my code for that as well:

// Your GPRS credentials (leave empty, if not needed)
const char apn[]      = "internet.apn"; // APN (example: internet.vodafone.pt) use https://wiki.apnchanger.org
const char gprsUser[] = ""; // GPRS User
const char gprsPass[] = ""; // GPRS Password

// SIM card PIN (leave empty, if not defined)
const char simPIN[]   = "0000"; 

// Server details
// The server variable can be just a domain name or it can have a subdomain. It depends on the service you are using
const char server[] = "20.43.**.**"; // domain name: example.com, maker.ifttt.com, etc
const char resource[] = "/api/v1/position_data";         // resource path, for example: /post-data.php
const int  port = 443;                             // server port number

// TTGO T-Call pins
#define MODEM_RST            5
#define MODEM_PWKEY          4
#define MODEM_POWER_ON       23
#define MODEM_TX             27
#define MODEM_RX             26
#define I2C_SDA              21
#define I2C_SCL              22

// Set serial for debug console (to Serial Monitor, default speed 115200)
#define SerialMon Serial
// Set serial for AT commands (to SIM800 module)
#define SerialAT Serial1

// Configure TinyGSM library
#define TINY_GSM_MODEM_SIM800      // Modem is SIM800
#define TINY_GSM_RX_BUFFER   1024  // Set RX buffer to 1Kb

// Define the serial console for debug prints, if needed
//#define DUMP_AT_COMMANDS

#include <Wire.h>
#include <TinyGsmClient.h>

#ifdef DUMP_AT_COMMANDS
  #include <StreamDebugger.h>
  StreamDebugger debugger(SerialAT, SerialMon);
  TinyGsm modem(debugger);
#else
  TinyGsm modem(SerialAT);
#endif

// I2C for SIM800 (to keep it running when powered from battery)
TwoWire I2CPower = TwoWire(0);

// TinyGSM Client for Internet connection
TinyGsmClient client(modem);

#define uS_TO_S_FACTOR 1000000UL   /* Conversion factor for micro seconds to seconds */
#define TIME_TO_SLEEP  3600        /* Time ESP32 will go to sleep (in seconds) 3600 seconds = 1 hour */

#define IP5306_ADDR          0x75
#define IP5306_REG_SYS_CTL0  0x00

bool setPowerBoostKeepOn(int en){
  I2CPower.beginTransmission(IP5306_ADDR);
  I2CPower.write(IP5306_REG_SYS_CTL0);
  if (en) {
    I2CPower.write(0x37); // Set bit1: 1 enable 0 disable boost keep on
  } else {
    I2CPower.write(0x35); // 0x37 is default reg value
  }
  return I2CPower.endTransmission() == 0;
}

void setup() {
  // Set serial monitor debugging window baud rate to 115200
  SerialMon.begin(115200);


  // Keep power when running from battery
  bool isOk = setPowerBoostKeepOn(1);
  SerialMon.println(String("IP5306 KeepOn ") + (isOk ? "OK" : "FAIL"));

  // Set modem reset, enable, power pins
  pinMode(MODEM_PWKEY, OUTPUT);
  pinMode(MODEM_RST, OUTPUT);
  pinMode(MODEM_POWER_ON, OUTPUT);
  digitalWrite(MODEM_PWKEY, LOW);
  digitalWrite(MODEM_RST, HIGH);
  digitalWrite(MODEM_POWER_ON, HIGH);

  // Set GSM module baud rate and UART pins
  SerialAT.begin(115200, SERIAL_8N1, MODEM_RX, MODEM_TX);
  delay(3000);

  // Restart SIM800 module, it takes quite some time
  // To skip it, call init() instead of restart()
  SerialMon.println("Initializing modem...");
  modem.restart();
  // use modem.init() if you don't need the complete restart

  // Unlock your SIM card with a PIN if needed
  if (strlen(simPIN) && modem.getSimStatus() != 3 ) {
    modem.simUnlock(simPIN);
  }

  // Configure the wake up source as timer wake up  
  esp_sleep_enable_timer_wakeup(TIME_TO_SLEEP * uS_TO_S_FACTOR);
}

void loop() {
  SerialMon.print("Connecting to APN: ");
  SerialMon.print(apn);
  if (!modem.gprsConnect(apn, gprsUser, gprsPass)) {
    SerialMon.println(" fail");
  }
  else {
    SerialMon.println(" OK");
    
    SerialMon.print("Connecting to ");
    SerialMon.print(server);
    if (!client.connect(server, port)) {
      SerialMon.println(" fail");
    }
    else {
      SerialMon.println(" OK");
    
      // Making an HTTP POST request
      SerialMon.println("Performing HTTP POST request...");
      // Prepare your HTTP POST request data
      String httpRequestData = "{\"latitude\":\"5656\",\"longitude\":\"5656\",\"altitude\":\"5656\",\"speed\":\"5656\",\"deviceId\":\"111112222200000\"}";
    
      client.print(String("POST ") + resource + " HTTP/1.1\r\n");
      client.print(String("Host: ") + server + "\r\n");
      client.println("Connection: close");
      client.println("Content-Type: application/json");
      client.print("Content-Length: ");
      client.println(httpRequestData.length());
      client.println();
      client.println(httpRequestData);

      unsigned long timeout = millis();
      while (client.connected() && millis() - timeout < 10000L) {
        // Print available data (HTTP response from server)
        while (client.available()) {
          char c = client.read();
          SerialMon.print(c);
          timeout = millis();
        }
      }
      SerialMon.println();
    
      // Close client and disconnect
      client.stop();
      SerialMon.println(F("Server disconnected"));
      modem.gprsDisconnect();
      SerialMon.println(F("GPRS disconnected"));
    }
  }
  // Put ESP32 into deep sleep mode (with timer wake up)
  esp_deep_sleep_start();
}

I successfully connect to the mobile network. The difference here is that I had to use the IP address of my server in order to connect to it. I've I used the URL as the one in the Wifi code but it never connects to the server. So I connect to the server as well but when I try to post JSON to the api endpoint nothing happens and there is no error as well. So my best guess is that the problem is somewhere aroung here:

   // Making an HTTP POST request
      SerialMon.println("Performing HTTP POST request...");
      // Prepare your HTTP POST request data
      String httpRequestData = "{\"latitude\":\"5656\",\"longitude\":\"5656\",\"altitude\":\"5656\",\"speed\":\"5656\",\"deviceId\":\"111112222200000\"}";
    
      client.print(String("POST ") + resource + " HTTP/1.1\r\n");
      client.print(String("Host: ") + server + "\r\n");
      client.println("Connection: close");
      client.println("Content-Type: application/json");
      client.print("Content-Length: ");
      client.println(httpRequestData.length());
      client.println();
      client.println(httpRequestData);

This is the serial output:

Initializing modem...
Connecting to APN: internet.a1.bg OK
Connecting to 20.43.**.** OK
Performing HTTP POST request...

Server disconnected
GPRS disconnected

Can anyone help to solve this problem, because I defenetly can't solve it on my own?
Thanks!