Onboarding Defender on Hyper V Server 2019, failing with error [Error Id: 15, Error Level: 1]

hey mate, so, apologies if i'm telling you to suck eggs here and you alrady did this. but I've gone round in circles 3 times now, trying to deploy on a 2012 R2 server (yea, EOSL and all that, I know, anyways.)

I went to Defender, Settings > Endpoints > Onboarding and set "Server 2012, Local script"
thought "nah it's just one computer, I don't need the installation package,I'll just get the onboarding package."

3 times now, I've ignored the "installation package" and just got the onboarding package and got the same error as you. no Sense Service. racking my brain, stepped through the script line by line. validated all te registry settings, deleted all the registry settings, rebooted, tried again. Still no sense service.

I'm making my fourth attempt now. Downloaded the installation package. Ran it.
Now i can see Service Control Manager installing the Sense Service.
Re-ran the script.

Onboarded successfully.

So, if you're using down-level server OS and you haven't already checked that you ran the installation package as WELL as the onboarding package, start there. Of course, if you HAVE done this, then just ignore me