Failed Serial Transmission Arduino-Node RED: COM4 Access Denied

Hi everyone. I'm struggling with this problem: I have programmed my Arduino Uno for trasmitting via USB Serial communication the temperature measured by a temperature sensor connected to one of the Analog inputs of the Arduino board. The port used for serial transmission is COM4. Opening the Serial Monitor of Arduino, I have verified the Arduino-side serial transmission occurs correctly.
I'd like to display the transmitted info into the debug of Node Red: I've used and connected "Serial In" and "debug" nodes between them. The problem is that when I deploy everything, "serial port COM4 error: Error: Opening COM4: Access denied" error displays. I can't understand what the problem is and how to solve it.
Thanks to who will try to help me!

Did you close the Arduino ide?
Verify if this is the correct comport in Windows device manager.

I forgot to write it. Anyway yes, I closed the Arduino Ide.
After programming Arduino, I first closed the Arduino IDE and then I launched Node RED.

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