How to set up rs232 serial communication with Primare SPA20 surround receiver

Hi all
i am completely new to Home Assistant, and to home automation as general. I run Home assistant on a raspberry pi 3b. Im new to this hardware as well. I was able to set up some basic integrations and automations in HA, like some lights, switches, controlling smart tv, my squeezebox touch, etc. I have a Primare SPA20 surround receiver with an RS232 serial port on it. After some research i found it can be connected to a home automation system. I really would like to integrate some of its basic functions to my Home assistant, like turn the amp on/off, monitoring its state (is it on or in standby) and use it to start some of my automations (turn on/off lights, start plazing music etc.). If someone could help me with a walktrough how to do this, i would be more than happy and thankful. I googled and googled and googled some more, and found some information about how to do this in Open HAB, but not in Home Assistant. I know nothing about serial communication. I bought a USB to rs232 adapter cable and a nullmodem cable, installed Node-Red, but cant really figure out how to communicate with the primare.
Some information i got from Primare.net:

Command structure
Commands are sent to the device using the following format, where each field is one byte sent to the device:
[]
The can be either ‘W’ for write or ‘R’ for read. The variable table that follows specifies which variables supports which types.
If verbose is active, the device will send replies on the following format either when a command is received or when the variable in question is changed on the device.
[]
Note that the field can contain several bytes of data for certain commands.
Command special chars
= 0x02
= 0x10
= 0x03
Write = 0x57 (ASCII: W)
Read = 0x52 (ASCII: R)
Escape sequence
If any variable or value byte is equal to , this byte must be sent twice to avoid confusing this with end of message.
Protocol settings
Baud rate: 4800
Bits: 8
Stop bits: 1
Parity: None
Example
The specific variables and commands will be defined later, here are examples on what the
commands looks like in bytes.
Command to toggle verbose setting. Command is write, variable is 13 (0x0d) and value is
0.
0x02 0x57 0x0xd 0x00 0x10 0x03

Hooked up the amp to the Rpi, set up connection with Node Red, but no response from the amp.

Than i found this this guide, wich confused me even more : Primare - Bindings | openHAB
He is using some commands instead of HEX code.

Hope someone can help me with this