Sample "callautomation-openai-sample-csharp" does not play audio

> Please provide us with the following information:
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### This issue is for a: (mark with an `x`)
```
- [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
> Clone the repo, open sample callautomation-openai-sample-csharp, fill the values in appsettings.json and follow exactly the steps as described. All reosurce are created successfully. EventGrid incoming call event is received. Call is connected.
But then when audio should be played to the user a PlayFailed event is received with status code: 8536 and message "Action failed, file could not be downloaded".
To test the phone calling we have 2 phone numbers in azure and from one number we call the other.

App Settings Variables look like following:
"AcsConnectionString": "endpoint=https://{ name }>.europe.communication.azure.com/;accesskey={ accesskey }" - copied from azure.portal
"CognitiveServiceEndpoint": "https://{ name }>.cognitiveservices.azure.com/",

### Any log messages given by the failure
>staus code 8536 and message "Action failed, file could not be downloaded"

### Expected/desired behavior
> The audio text should be played and shouldn't receive PlayFailed event.

### OS and Version?
> Windows 10

### Versions
>

### Mention any other details that might be useful

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> Thanks! We'll be in touch soon.

Reproduce the failure in the callautomation-openai-sample-csharp sample after filling appsettings.json and following the documented steps. Start by tracing the incoming call, connection, and PlayFailed event with status 8536; done means the sample plays the audio without receiving the file-download failure.

Written by the indexing model from the issue text.