Modbus Slave simulator setup

Hi everyone. I am trying to setup a modbus slave simulator in my PC in order to test my Python script before I purchase an actual hardware for the prototyping. I am facing issue trying to setup this simulator and hope someone who have experience with this can point me to the right direction.

My current understanding of setting up the simulator is this:

1. Turn on the simulator software
2. Setup the connection
3. Test my script by connecting to the simulator

I am using a software called "Modbus Slave". When I setup the connection, using "Serial Port", it often tells me "Port n not available". I have read the documentation and don't whether I need to have a physical RS485-USB converter connected to my PC to make the port available. What is the proper way to setup the simulator with serial connection?

Note: the simulator will be a slave device, and my Python script will run and take the registry value from this simulator.

Any help will be appreciated!
I'll try,
(1) install the SW, it will give you some trial version. I think it should be enough.
(2) Create New Pair, the SW will open for you 2 virtual comm ports that are logically connected between them.
* follow the following link:
(3) you can connect python to one virtual comm port, and modbus slave to the other. and it should communicate between them through the virtual comm pair.

Hope this helps.