SIM900/Arduino UNO R3 serial communication not working For some reason I cannot establish serial connection between the two devices. The shield is connected to the network because my number can be called, but I cannot send it any commands via the serial.
I tried several ways to wire it up:
shield rx&amp;tx (the ones that require female jumper) to 7 &amp; 8 of arduino, declaring 7 &amp; 8 in the serial.
shield pins 7 &amp; 8 (they have (serial) as label) to 7 &amp; 8 of arduino, declarting 7 &amp; 8 in the serial.
shield rx&amp;tx the little holes to 7 &amp; 8 of arduino, declaring 7 &amp; 8 in the serial.
Tried even different pins other than 7 &amp; 8. None worked.
I'm powering the shield with 12v transformator that can provide up to 3Ah and the arduino is connected to laptop.
Any suggestions ?
Here's the code:

#include &lt;SoftwareSerial.h&gt;

//Create software serial object to communicate with SIM900
SoftwareSerial mySerial(7, 8); //SIM900 Tx &amp; Rx is connected to Arduino #7 &amp; #8

void setup()
{
  //Begin serial communication with Arduino and Arduino IDE (Serial Monitor)
  Serial.begin(9600);

  //Begin serial communication with Arduino and SIM900
  mySerial.begin(9600);

  Serial.println("Initializing..."); 
  delay(1000);

  mySerial.println("AT"); //Handshaking with SIM900
  updateSerial();

  mySerial.println("AT+CMGF=1"); // Configuring TEXT mode
  updateSerial();
  mySerial.println("AT+CMGS=\"+ZZxxxxxxxxxx\"");//change ZZ with country code and xxxxxxxxxxx with phone number to sms
  updateSerial();
  mySerial.print("Last Minute Engineers | lastminuteengineers.com"); //text content
  updateSerial();
  mySerial.write(26);
}

void loop()
{
}

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


And also, why are there so many RX/TX on the shield ? I see RXD/TXD and RX/TX.
To make everything work fine with this exact code and wiring from the lastminuteengineers, you need to change the jumper (black plastic piece) position in J11. it has to connect the pins D8(RX) and D7(TX), which are the pins at the top of the yellow plate, to the two pins in the middle of the yellow plate.