How to configure monitoring of discourse-prometheus on prometheus

I have installed discourse and discourse-prometheus plugins, then I add the following configuration in prometheus.yaml:

- job_name: forums
  metrics_path: /metrics
  static_configs:
    - targets:
      - forums.kingsd.top
  scheme: https
  basic_auth:
    username: admin
    password: password

Then I found that the status of the corresponding Endpoint on prometheus was always DOWN, and the error log server returned HTTP status 404 Not Found appeared

The following error log keeps showing up in shared/standalone/log/rails/production.log:

Started GET "/metrics" for 123.184.31.122 at 2022-03-17 11:03:34 +0000
ActionController::RoutingError (No route matches [GET] "/metrics")
config/initializers/100-quiet_logger.rb:23:in `call'
config/initializers/100-silence_logger.rb:31:in `call'
lib/middleware/enforce_hostname.rb:23:in `call'
lib/middleware/request_tracker.rb:202:in `call'
  Rendered exceptions/not_found.html.erb within layouts/no_ember (Duration: 0.3ms | Allocations: 193)
  Rendered layout layouts/no_ember.html.erb (Duration: 4.1ms | Allocations: 2216)
  Rendered html template (Duration: 0.0ms | Allocations: 2)

Is there something wrong with my configuration? please help me.

Sorry, I forgot to configure DISCOURSE_PROMETHEUS_TRUSTED_IP_ALLOWLIST_REGEX