API on Groupshare 2020, HTTP request used to publish a Studio package to an empty server project. 500 Internal Server Error

I am trying to call 

http://%HOST%/projectserver/api/1.0/projects/[projectid]/publishpackage?callbackUrl=[url]

but I cannot manage to make it work

The request:

POST /api/projectserver/v2/projects/fcb519b7-5a93-46a1-a318-19c177f060ed/publishpackage? HTTP/1.1
Host: http://zdc-sdl-app2020:41234
Authorization: Bearer <token>

----WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="file"; filename="/C:/Temp/Project 1.sdlppx"
Content-Type: 

(data)
----WebKitFormBoundary7MA4YWxkTrZu0gW

And I get an 500 Internal Server Error

{"Message":"An error has occurred."}

We have just installed our Groupshare server 2020

UI: 15.1.0
GS: 15.1.0.3172 - GS 2020 SR1