We have found that if Machine Transcription is not working for a customer that they will need to add our servers to their "Allow List" with /azure.
bsk-ml-eastus-signalr-webapp-prod-001.azurewebsites.net (it is an azure webapp) – which is necessary for Transcription services to work. The protocol that is used is WSS (WebSocketsSecure) to the 443 port. So, the whole request might be appearing in the firewall logs as: “wss://bsk-ml-eastus-signalr-webapp-prod-001.azurewebsites.net/”.
Once they added this URL to their Allow List, transcriptions worked immediately.