Hello, I am trying to reproduce the following code to communicate in serial.

https://www.industrialshields.com/es_ES/blog/blog-industrial-open-source-1/post/como-utilizar-la-libreria-de-software-serial-en-el-controlador-industrial-arduino-plc-99

On the M-Duino 38R + the RX (SO), TX (SI) pins are respectively 50, 51

So, I wired tx from the device to RX MDuino and rx from the device to tx from MDuino

For information, here is the device with which I tried to communicate with M-Duino : https://learn.sparkfun.com/tutorials/sparkfun-rfid-starter-kit-hookup-guide

//  https://github.com/PaulStoffregen/SoftwareSerial
#include <SoftwareSerial.h>
 

// https://github.com/agmangas/SerialRFID
#include <SerialRFID.h>

const byte RX_PIN = 50;//PIN_SPI_MISO;
const byte TX_PIN = 51;//PIN_SPI_MOSI;

SoftwareSerial sSerial(RX_PIN, TX_PIN); // RX (SO), TX (SI)
SerialRFID rfid(sSerial);

char tag[SIZE_TAG_ID];
char matchTag[SIZE_TAG_ID] = "5C00CADB5A17";


//SoftwareSerial mySerial(50, 51); // RX (SO), TX (SI)

void setup()
{
    Serial.begin(9600);
    sSerial.begin(9600);
    Serial.println();
    Serial.println(">> Starting SerialRFID example program");
}

void loop()
{
    if (rfid.readTag(tag, sizeof(tag)))
    {
        Serial.print("Tag: ");
        Serial.print(tag);
        Serial.println();

        //if (SerialRFID::isEqualTag(tag, matchTag))
        //{
        //    Serial.println(" / Match: OK");
        //}
        //else
        //{
        //    Serial.println(" / Match: No");
        //}
    }
}

I tested the following code on the arduino mega (basic) and it works ...

Response arduino mega (basic)
>> Starting SerialRFID example program
Tag: 4300926D45F9
Tag: 4300926D45F9

Is there something I don't understand?

Thank you in advance for your answer.