Can read Serial but cannot write - serial communication Arduino Mega 2560 clone

Question

I am having issues using the following USB to UART module. I am using an Arduino 2560 clone.

I have two connections with the Arduino:

1. COM7 which consists of the given module, connected to the main Rx0/Tx0 on the Arduino, with yellow to Tx0, orange to Rx0 and ground to the Arduino ground.
2. COM4 which consists of a usual USB to USB module, connected to the Arduino's USB port.

I can read from the Arduino perfectly fine using either COM4 or COM7, but I cannot send data through the serial or upload a program to it through COM7, only through COM4.

I have tried the following for uploading data with COM7: PuTTY and Arduino Serial.

Once again: The Arduino can correctly receive a program file or read serial input data from COM4, it correctly outputs data to either COM4 or COM7, but I cannot upload data to it from COM7.

Code I am using to test the COM7's ability to send data:

int incomingByte = 0; // for incoming serial data

void setup() {
  Serial.begin(9600); // opens serial port, sets data rate to 9600 bps
}

void loop() {
  // send data only when you receive data:
  if (Serial.available() > 0) {
    // read the incoming byte:
    incomingByte = Serial.read();

    // say what you got:
    Serial.print("I received: ");
    Serial.println(incomingByte, DEC);
  }
}