void setup() {
  Serial.begin(115200);                
  Serial2.begin(115200, SERIAL_8N1, 11, 10);
  Serial1.begin(115200, SERIAL_8N1, 38, 1);
}

void loop() {
  // Check if Serial1 has received any data
  if (Serial1.available()) {
    char byteReceived1 = Serial1.read();
    Serial.print("Byte received on Serial1: ");
    Serial.println(byteReceived1);
  }

  // Check if Serial2 has received any data
  if (Serial2.available()) {
    char byteReceived2 = Serial2.read();
    Serial.print("Byte received on Serial2: ");
    Serial.println(byteReceived2);
  }

  // Call the functions to send "H" and "I"
  sendHOverSerial1();
  sendIOverSerial2(); // Stops sendHOverSerial1() working
}

void sendHOverSerial1() {
  Serial1.begin(115200, SERIAL_8N1, 38, 3); // Re-initialize Serial1 with different pins
  Serial1.write("H"); 
  delay(1000); 
 Serial1.begin(115200, SERIAL_8N1, 38, 1); // Initialize Serial1 back to stock pins
}

void sendIOverSerial2() {
  Serial2.begin(115200, SERIAL_8N1, 47, 21);  // Initialize Serial2 with pin swap 
  Serial2.write("I"); 
  delay(1000); 
  // Serial2.begin(115200, SERIAL_8N1, 11, 10); // <------- causes panic
}