C# - Printing Receipt

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C#

printing

I just installed my EPSON TM-T90 Receipt and I wanna test it using C#.
I tried googling it, but haven't learned much about it...

What I want to do is simply print a line of code, for example "Hello World".
I tried using the following:

char esc = (char)27;
char ff = (char)12;
SerialPort port = new SerialPort("COM3", 19200, Parity.None, 8, StopBits.One);
port.Open();
port.Write(esc + "@Hello World!" + ff);
port.Close();

Yet it says that access to COM3 was denied.
It's installed, I used the official advanced driver that installed everything, it's showing in my available printers and when I installed it I selected the correct port which is COM3 and configured the Serial Interface already.