Call Automation - Outbound Call Sample does not work

> Please provide us with the following information:
> ---------------------------------------------------------------

## Setting:
I have tried to run the [Call Automation - Quick Start Sample](https://github.com/Azure-Samples/communication-services-python-quickstarts/tree/main/callautomation-outboundcalling), but could not get it to do anything, but immediately disconnect when I try to make an outbound call.

### This issue is for a: (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [ ] feature request
- [X] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

### Minimal steps to reproduce
- install the demo by cloning the repo
- edit the required variables, in my case they look now something like this:
- ACS_CONNECTION_STRING = "endpoint=https://xxx.germany.communication.azure.com/;accesskey=xxxx"
- ACS_PHONE_NUMBER = "+4940****"
- TARGET_PHONE_NUMBER = "+4940***" (this is a Teams phone number, I also tried other numbers)
- CALLBACK_URI_HOST = "https://xxxxx.euw.devtunnels.ms:8080" (as produced by my devtunnel)
- COGNITIVE_SERVICES_ENDPOINT = "https://xxxx.cognitiveservices.azure.com/"

### Any log messages given by the failure
```[2024-02-02 13:57:59,545] INFO in main: Created call with connection id: 531f5e00-c5f3-4a9f-a20c-65ab6f6edf55 to +494023778954
127.0.0.1 - - [02/Feb/2024 13:57:59] "GET /outboundCall HTTP/1.1" 302 -
127.0.0.1 - - [02/Feb/2024 13:57:59] "GET / HTTP/1.1" 200 -
[2024-02-02 13:58:00,459] INFO in main: Microsoft.Communication.CallDisconnected event received for call connection id: xxxx
[2024-02-02 13:58:00,459] INFO in main: Event type: Microsoft.Communication.CallDisconnected, data: {'version': '2023-10-15', 'callConnectionId': 'xxxx', 'correlationId': 'yyyy', 'publicEventType': 'Microsoft.Communication.CallDisconnected'}
127.0.0.1 - - [02/Feb/2024 13:58:00] "POST /api/callbacks HTTP/1.1" 200 -
```

### Expected/desired behavior
The outbound call connects to the target number.

### OS and Version?
Linux

### Versions
Python 3.9.18

`pip list` produces:

Package Version
---------------------------------- ----------
azure-communication-callautomation 1.1.0
azure-core 1.29.7
azure-eventgrid 4.11.0
blinker 1.7.0
certifi 2023.11.17
charset-normalizer 3.3.2
click 8.1.7
Flask 3.0.1
idna 3.6
importlib-metadata 7.0.1
isodate 0.6.1
itsdangerous 2.1.2
Jinja2 3.1.3
MarkupSafe 2.1.4
pip 23.0.1
requests 2.31.0
setuptools 58.1.0
six 1.16.0
typing_extensions 4.9.0
urllib3 2.1.0
Werkzeug 3.0.1
zipp 3.17.0

### Mention any other details that might be useful
I would assume that is has something to do with out setup, but what could it be? I tried to find out whether there are any restrictions on making outbound calls in Germany, but it seems not so.

Further info:
- Data Location of our AZ Communication Service: Germany
- Our Phone number has Status "Active", Type "Local, DE", no SMS features, Calling features: "Make, receive calls"
- I can receive calls on this phone number via the AZ Communication Service

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