Linux Client Daemon installation

I've got a windows server with a license and a linux client where the can be run manually using the -n option and everything works fine. What i'd like to do now is setup the linux server so that i don't have to ssh in and start the client each time it needs to be rebooted. To do that it needs to be installed as a daemon which is a supported configuration and there's a near guide about it at https://virtualhere.com/client_service but i can't work out what to do with the script provided.

The os is debian 10.5 which is what is required for the HomeAssistant installation I'm working on so I can't change os or massively reconfigure everything. I've downloaded the script in the linked article above and it isn't a Unit file which is one of the ways i've found to install services, the syntax is all wrong for that. I thought that it might be a script that can be used with init.d but when i try to configure it to be used with update-init-d the resulting service is marked as bad by the os.

Can point me at, or give me some instructions, on how to use the provided file on debian 10.5 please?