PATCH /api/v2/conversations/voice/{id} 404 on participant attributes

Trying to update participant attributes on a live voice call using the Conversations API. I’m sending a PATCH request to /api/v2/conversations/voice/{conversationId} with the participant ID and new attributes in the body. Getting a 404 Not Found error. The conversation exists and is active. Is the endpoint different for voice? Here is the payload:

{"participants": [{"id": "p123", "attributes": {"key": "value"}}]}

Checked the docs but voice seems vague.