code: def infer_msg(self, tts, rsp):
          
          # rsp should be <requests.Response>
          # http://docs.python-requests.org/en/master/api/
          status = rsp.status_code
          reason = rsp.reason
  
          cause = "Unknown"
          if status == 403:
              cause = "Bad token or upstream API changes"
          elif status == 404 and not tts.lang_check:
              cause = "Unsupported language '%s'" % self.tts.lang
          elif status >= 500:
              cause = "Uptream API error. Try again later."
  
          return "%i (%s) from TTS API. Probable cause: %s" % (
              status, reason, cause)
docs: Attempt to guess what went wrong by using known
          information (e.g. http response) and observed behaviour