AI-103: Developing AI Apps and Agents on Azure

When you call the Speech to text REST API for custom speech, you set the project property to the ID of your custom speech project — the GUID that appears in the fine-tuning URL in the Microsoft Foundry portal (for example, 00001111-aaaa-2222-bbbb-3333cccc4444). Microsoft's documentation explicitly warns that this custom speech project ID is NOT the same as the Microsoft Foundry project ID, so supplying the generic "project ID" (the Foundry project ID) is what produces the "project ID is invalid" error described, and you must use the custom speech project ID instead. The project URL and the custom speech endpoint URL are self/reference links returned in API responses rather than the value you assign to the project property, so neither the project URL nor the endpoint URL is correct.