code: public void sendDtmf(final String dtmf) throws IOException, AppPlatformException {
          final Map<String, Object> params = new HashMap<String, Object>();
          params.put("dtmfOut", dtmf);
  
          final String uri = StringUtils.join(new String[]{
                  getUri(),
                  "dtmf"
          }, '/');
          client.post(uri, params);
      }
docs: Sends DTMF.
  
  @param dtmf DTMF value
  @throws IOException unexpected error.
  @throws AppPlatformException unexpected exception.