[Python] Conference not listed when created via Twiml Callback

I configured a phone number, so that an incoming call triggers an HTTP callback. On my server I am running a Python script which listens for that callback and answeres with a "dial conference command".

That works fine. When I call my phone number I join the conference and I can hear the conference wait music. Another call also works and the two calls come together in the conference and can talk to each other. But when using client.conferences.list() I cannot see this conference.

1. 
   Python code listening for the callback:
   
   import os
   import sys
   import time
   import json
   import uvicorn
   
   from dotenv import load_dotenv
   from fastapi import FastAPI, WebSocket, Form, Request, Response, Query
   from fastapi.responses import HTMLResponse, JSONResponse
   from fastapi.middleware.cors import CORSMiddleware
   from loguru import logger
   from twilio.twiml.voice_response import VoiceResponse
   from twilio.rest import Client
   
   ###############################################################################
   # init
   ###############################################################################
   load_dotenv(f".env")
   
   app = FastAPI()
   
   app.add_middleware(
   CORSMiddleware,
   allow_origins=["*"], # Allow all origins for testing
   allow_credentials=True,
   allow_methods=["*"],
   allow_headers=["*"],
   )
   
   logger.remove()
   logger.add(sys.stderr, level="DEBUG")
   
   ###############################################################################
   # Routes and WebSocket
   ###############################################################################
   @app.post("/twilio-call")
   async def start_call(request: Request, AccountSid: str = Form(...), CallSid: str = Form(...), From: str = Form(...), To: str = Form(...)):
   # push into conference
   conference_room_name = "test-1234"
   logger.info(f"|{CallSid}| Caller joins conference room {conference_room_name}")
   response = VoiceResponse()
   dial = response.dial()
   dial.conference(conference_room_name)
   
   logger.info(f"|{CallSid}| xml=" + str(response))
   return Response(str(response), media_type='text/xml')
   
   ###############################################################################
   # main
   ###############################################################################
   if __name__ == "__main__":
   app_port = int(os.getenv("APP_PORT"))
   
   uvicorn.run(app, host="0.0.0.0", port=app_port)
   
   
   When calling, I can see in my console:
   
   INFO: Started server process [1023305]
   INFO: Waiting for application startup.
   INFO: Application startup complete.
   INFO: Uvicorn running on http://0.0.0.0:3001 (Press CTRL+C to quit)
   2025-09-09 16:23:44.896 | INFO | __main__:start_call:41 - |CA572e178803ea4e8d6b3f242a2ac03b58| Caller joins conference room test-1234
   2025-09-09 16:23:44.897 | INFO | __main__:start_call:46 - |CA572e178803ea4e8d6b3f242a2ac03b58| xml=<?xml version="1.0" encoding="UTF-8"?><Response><Dial><Conference>test-1234</Conference></Dial></Response>
   INFO: 108.130.4.158:0 - "POST /twilio-call HTTP/1.1" 200 OK
   
   
   and I hear the conference wait music.
   
   
2. 
   List conferences
   
   While staying in the conference I use the following code to list all conferences:
   
   from twilio.rest import Client
   from twilio.twiml.voice_response import VoiceResponse
   from dotenv import load_dotenv
   import os
   
   # init
   env = os.getenv("ENVIRONMENT", "dev")
   load_dotenv(f".env.{env}")
   
   account_sid = os.environ.get("TWILIO_ACCOUNT_SID", "")
   auth_token = os.environ.get("TWILIO_AUTH_TOKEN", "")
   conference_room_name = "test-1234"
   
   # create client
   client = Client(account_sid, auth_token)
   
   # list conferences
   print("Conference-List:")
   conferences = client.conferences.list()
   for conf in conferences:
   print(f"SID: {conf.sid} | FriendlyName: {conf.friendly_name} | DateCreated: {conf.date_created} | Status: {conf.status}")
   
   
   Result: no conferences found.
   
   
3. 
   But when using this code to initiate an outbound call, the conference is listed
   
   from twilio.rest import Client
   from twilio.twiml.voice_response import VoiceResponse
   from dotenv import load_dotenv
   import os
   
   # Init
   load_dotenv(f".env")
   
   account_sid = os.environ.get("TWILIO_ACCOUNT_SID", "")
   auth_token = os.environ.get("TWILIO_AUTH_TOKEN", "")
   conference_room_name = "test-1234"
   
   # Twilio Client
   client = Client(account_sid, auth_token)
   
   # Outbound Call with TwiML to join conference
   call = client.calls.create(
   to="+49...",
   from_="+49...",
   twiml=f'''
   <Response>
   <Dial>
   <Conference>{conference_room_name}</Conference>
   </Dial>
   </Response>
   '''
   )
   
   input("Press Enter to list conferences...")
   
   print("Conference-List:")
   conferences = client.conferences.list()
   for conf in conferences:
   print(f"SID: {conf.sid} | FriendlyName: {conf.friendly_name} | DateCreated: {conf.date_created} | Status: {conf.status}")
   
   
   Output:
   
   Press Enter to list conferences...
   Conference-List:
   SID: CF82fd459cce185021d6e18e18141c8c0e | FriendlyName: test-1234 | DateCreated: 2025-09-09 16:40:23+00:00 | Status: in-progress

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