SerialArduinoTest.ino

#include <SoftwareSerial.h>

SoftwareSerial Bt(49, 8);
String msg;

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

void loop() {

  while(Bt.available()) {
    delay(1);
    char c = Bt.read();
    msg += c;
  }

    
  while(Serial.available()) {
    delay(3);
    char c = Serial.read();
    Bt.print(c);
  }

  if(msg.length() > 0) {
    Serial.println(msg);
    msg = "";
  }

}