Pengines issue

I’m using: SWI-Prolog version 8.0.3, via pengines on docker

Gundam:my_codes andreacortis$ docker run -p -i -d -t pengines

Gundam:my_codes andreacortis$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
c988c1b8f54e        pengines            "swipl --p…"   16 minutes ago      Up 16 minutes>3030/tcp   elegant_noether

the server is up and running

Gundam:my_codes andreacortis$ curl
<!DOCTYPE html>
<html lang="en">
      <!-- Meta, title, CSS, favicons, etc. -->
      <meta charset="utf-8">
      <meta name="viewport" content="width=device-width, initial-scale=1.0">
      <meta name="description" content="">
      <meta name="author" content="">

I want the code to: reproduce the example at

by using these commands in python:

from pengines.Builder import PengineBuilder 
from pengines.Pengine import Pengine 
pengine_builder = PengineBuilder(urlserver="") 

In [20]: pengine = Pengine(builder=pengine_builder,slave_limit=1, debug=True)                                                                   
Starting call.
Starting post request with URL, content_type: application/json, and body: {"chunk": 100, "format": "json"}
Starting Post request.
URL is:
Data (body) :  b'{"chunk": 100, "format": "json"}'
Headers:  {'User-Agent': 'PythonPengine', 'Accept': 'application/json', 'Accept-Language': 'en-us,en;q=0.5', 'Content-type': 'application/json'}
response_string is : {
{'event': 'create', 'id': '84ec823c-c2dc-4993-86f5-7d64d8ee996f', 'slave_limit': 3}
Initialization complete.

In [21]: query = "X = 3, writeln(X)" 
    ...: pengine.ask(query) 
    ...: print(pengine.currentQuery.availProofs)                                                                                                
Starting the call to ask.
Current state is idle
Initializing query with query: X = 3, writeln(X)
Call to ask is complete

I am not getting anything back and I do not understand if this is a prolog issue or a python issue.

By the way, I also get an empty list by trying the query

query = "member(X, [1,2,3])"

or any other query.

Any advice, please?