Lendo TAG RFID

#include <SoftwareSerial.h>

#define ADD_TAG_CODE "1F001F9CE37F"  //Definindo a TAG
SoftwareSerial rfid = SoftwareSerial(4, 5);

void setup(){
  Serial.begin(9600);
  Serial.println("Serial Ready");

  rfid.begin(9600);
  Serial.println("RFID Ready");
}



void loop() {
  char c = "";
  String msg ="";


  
  while (rfid.available() > 0){
    c = rfid.read();
    msg += c; 
  }
  
  msg = msg.substring(1, 13);
  Serial.println(msg);

  if(msg=="1F001F9CE37F"){
    Serial.println("okkkk");
  }
  

delay(1000);
}