Sim800l doesn't respond to AT commands

Question

My SIM800L doesn't respond to AT commands. The serial monitor is simply blank.

And the led blinks every 3 seconds which means it is connected to a network

I power it through an LM2596 buck down converter with 4.0 v (I've tried to power with voltages until 4.4v), From a 12v power supply.

Can you help me? (Please keep in mind that I'm an absolute beginner in this field. Thanks)

I used this wiring diagram from Last Minute Engineers. my circuit diagram

And also their code:

#include <SoftwareSerial.h>
 
SoftwareSerial mySerial(3, 2); //SIM800L Tx & Rx is connected to Arduino #3 & #2 
void setup() { 
 Serial.begin(9600);
 mySerial.begin(9600); 
 Serial.println("Initializing..."); 
 delay(1000);
 mySerial.println("AT");
 updateSerial(); 
 mySerial.println("AT+CMGF=1");
 updateSerial(); 
 mySerial.println("AT+CNMI=1,2,0,0,0"); 
 updateSerial(); 
} 
void loop() 
{ 
 updateSerial();
} 
void updateSerial() { 
 delay(500); 
 while (Serial.available()) { 
 mySerial.write(Serial.read());
 } 
 while(mySerial.available()) { 
 Serial.write(mySerial.read());
 }
}

• Fahad: Check the Tx and Rx wiring carefully. Do the Arduino Tx and Rx LEDs blink?
• Ângela Sulissa: Yes. I used the same wiring diagram with a GPS module (minus the resistors) and it worked fine