Graylog send log forwarder to logstash

I would like to use Graylog forwarder log to Logstash. Has anyone ever done this? Now I’m encountering this error. The output cannot be connected to Logstash.
Graylog version Graylog 5.1.5+993cd0f

hey @thanarat

I have not.

I think it forwards to Graylog server not to logstash.