Arduino mega SIM800l special characters

Question

I have a problem with the Arduino mega board and the SIM800L module I connect to the RX and TX pins of the module and when I enter the serial monitor it returns these characters, what could it be?

void setup() {
  Serial.begin(9600);

  //Begin serial communication with Arduino and SIM800L
  Serial1.begin(9600);

}

void loop() {
  delay(500);
  while (Serial.available()) {
    Serial1.write(Serial.read()); //Forward what Serial received to Software Serial Port
  }

  while(Serial1.available()) {
    Serial.write(Serial1.read()); //Forward what Software Serial received to Serial Port
  }

} 

Answer 1

After so much searching and looking on the oscilloscope I have found the solution, In case you are using a LM2596 buck converter to power up the module, remember to common all the ground of the circuit.