$speechContext = 'GenericHints'; // documentation point to Generic
        $response = $speechService->speechToTextCustom($speechContext, $voiceFilePath, null, null, null, 'pt-BR');

//return message
{"RequestError": {
             "ServiceException": {
             "MessageId": "SVC0002",
             "Text": "Invalid input value for message part %1" ,
             "Variables" : "Content-Language"}
            }}
         :400