code: public function fail(string $group, string $message)
      {
          if ($this->completed || $this->failed) {
              throw new JobAlreadyFinishedException();
          }
  
          $jsonData = json_encode($this->data, JSON_UNESCAPED_SLASHES) ?: '{}';
  
          $this->getEventsManager()->fire(new JobEvent\OnFailure($this, $this, $group, $message));
  
          $this->failed = true;
  
          return $this->client->fail($this->jid, $this->worker, $group, $message, $jsonData);
      }
docs: Mark the current Job as failed, with the provided group, and a more specific message.
  
  @param string $group   Some phrase that might be one of several categorical modes of failure
  @param string $message Something more job-specific, like perhaps a traceback.
  
  @return bool|string The id of the failed Job if successful, or FALSE on failure.