Arduino Duo Serial.available not working

Hardware Arduino Due
4

Hi all, here is my code

void setup() {
Serial.begin(9600);
SerialUSB.begin(9600);
Serial1.begin(9600);

}

void loop() {
if (Serial.available() > 0 ) {
Serial1.print("from serial available");
SerialUSB.print("from serial available");
}

if(SerialUSB.available() > 0 ){

Serial1.print("from serialUSB available");
Serial.print("from serialUSB available");
}

if(Serial1.available() > 0 ){
SerialUSB.print("from Serial 1 available");
Serial.print("from Serial 1 available");
}

delay(1000);
}

void serialEvent(){
Serial1.print("from serial event");
SerialUSB.print("from serial event");
}

At this point, I just wanted to print something whenever "Serial", port 1 is receive something.

I also upload the my wiring connection, basically I use TTL to RS232 convertor and use my laptop to send/receive the data