I believe the issue is related to 1) Creating a Managed Identity for Azure Communication Services, and 2) link ACS with Cognitive Services. In the navigation pane on the left, create a link between ACS and the defined Azure AI Services. One issue is that you can create "Speech Services" or recently renamed to "Azure AI Services". I choose AI Services as I may also use the other "Cognitive Services" that are under the umbrella of "Azure AI Services".
My issue is a random (?) time-out issue with Azure AI Text to Speech. One call works, and the next call, I get a timeout.