Call Azure Speech Service API using custom domain name

I've created an instance of Azure Speech Service and I'm trying to retrieve information using both "regional" url of the service and custom domain name (in the Azure portal I create a custom domain name but I leave "All networks" in the Networking blade).

I've tried to retrieve the list of available voices (from my local machine using postman):

• using "regional" endpoint (with my key in the header Ocp-Apim-Subscription-Key) https://northeurope.tts.speech.microsoft.com/cognitiveservices/voices/list -> everything works fine
• using the custom domain name (with my key in the header Ocp-Apim-Subscription-Key) https://{custom-domain-name}.cognitiveservices.azure.com/tts/cognitiveservices/voices/list -> I've got a 404
  
  I've tried to do a ping and a nslookup to {custom-domain-name}.cognitiveservices.azure.com and everything seems to be ok from that point of view.
  
  Any suggestions on what the problem could be? Thanks a lot

Call Azure Speech Service API using custom domain name

According to this MS-Document, Speech Services use custom subdomains with private endpoints only.

I followed this MS-Document , Created Speech service with custom domain and private endpoint.

I created private endpoint and Virtual Machine within the same VNet and subnet with cognitive service(speech) public access disabled.

Now, Inside Virtual machine I can able to retrieve the list of available voices using Custom domain.

Virtual machine: