No SQL Error, but still 500 on Prolog

Hey there!

I finally managed to install the OCSI on Ubuntu 20.04LTS
There are so many "HowTo" s but everyone is missing some parts. How ever.. the server is running right now. So far so good.
In my Test-environment I have 2 Clients (Both Windows 10 1909)
One Client does have a Sophos Home AV the other one just the windows Defender.

The one with the Sophos Protection won't talk fully to the OCSI Server. the Prolog conversation is starting but then only Code 515 with the ...;end;error at the end of the line.

The other System is getting 511 ...,deploy;no_file / 515 ...;end;bad_request / and 515 ...;end;error

Now I'm not sure what to do. I'm totally new to this Software and I want to bring it live.
Can someone help me?

btw. I already tried to install the whole system before on a 18.04 with a mariadb.. this did result in several SQL errors and even didn't work, as I inserted all correct credentials to all needed files.

[EDIT]

Now, sometimes, the Prolog works, the client sends it's Inventory Data. But, then at the end, it fails by "Download disabled by Server"
where can I enable this?

[/EDIT]